U.S. authorities are taking no chances with the prisoner they call Ramzi Ahmed Yousef.

They respect his alleged bomb-making prowess so much that they have gradually stripped him of all belongings. Since accusing him of building the bomb that blew up the World Trade Center in 1993, they have kept him under 24-hour observation at New York's Metropolitan Correctional Center, removing his wristwatch, toothpaste, shaving cream, coffee creamer, cup and spoon. For a few weeks, his jailers even took away his Koran -- until his lawyer raised a ruckus.

When he was arrested four months ago in Pakistan, little was known about the man who U.S. prosecutors say is responsible for the powerful explosion on Feb. 26, 1993, that killed six, injured a thousand and brought terrorism to the streets of New York. Since then, investigators on three continents have worked to fill the considerable holes in his biography. His movements, his motives, his nationality -- even his real name -- have become objects of the hunt.

The portrait is far from complete. Still, if information assembled by authorities in the United States, Pakistan, the Philippines, Saudi Arabia, Kuwait and Britain proves correct, Yousef would be one of the most traveled, audacious and ambitious terrorists of the 1990s. In the short span of four years, from early 1991 until his arrest, there is evidence that he carried out two other bombings in Iran and the Philippines, planned assassination attempts against Pope John Paul II and Pakistani Prime Minister Benazir Bhutto, and developed an elaborate but unrealized scheme to blow up 11 American commercial airplanes.

At first glance, the slender 27-year-old prisoner who sits quietly at court hearings hardly seems like a terrorist mastermind. But his words strike a strident, dangerous chord. He has pleaded not guilty to the charges against him in court, but he declared his support for the bombing in an interview he has given during his imprisonment.

In the interview, with a reporter for the Arabic-language London-based Al Hayat newspaper, Yousef described himself as an Islamic militant and declared his support of violence in pursuit of the Palestinian cause. "I support this movement's objectives, be they the {World Trade} Center or something else," according to a translation of the April 10 interview. "I believe that this movement, and Palestinians generally, is entitled to strike U.S. targets because the United States is a partner in crimes committed in Palestine."

Investigators and U.S. analysts are not ready to believe that Yousef is just another militant friend of Palestinians. They have pursued various theories about his motives: Is he a mercenary who hires himself out to militant groups? Is he part of a network of radical Islamic militants that traces its ideological origins to the Afghan mujaheddin -- resistance fighters who conducted a long-running war with the Afghan government and its patron, the former Soviet Union? Or is he an Iraqi terrorist agent avenging President Saddam Hussein's defeat in 1991 by the U.S. military?

Yousef rejected any ties to Saddam in the April interview. He called himself an "admirer" of the Afghan resistance movement and other groups that allied themselves with the mujaheddin cause. And he said he knows and admires Sheik Omar Abdel Rahman, an Egyptian-born cleric now on trial in New York for plotting a series of bombings. Abdel Rahman, who has served as an inspiration to Egypt's violent Islamic movement as well as to Arab veterans of the Afghan war, is said by prosecutors to have exhorted the group that set off the World Trade Center blast.

A six-week investigation by Washington Post reporters in Pakistan, the Philippines, Britain and the United States, including interviews and inspections of documents that have not been made public, found that Yousef's alleged activities fit a pattern of what U.S. officials are calling "a new breed of terrorist." His main goal,investigators say, seems to have been wreaking maximum destruction and damage to buildings and people -- as opposed to hijacking airplanes or taking hostages -- as a way to punish those he perceived to be the enemies of the Palestinians and Islam.

The Post reporters found little evidence that Yousef had developed any kind of sophisticated network. Instead, he seemed to have tapped into the resources of existing, local Islamic militant groups during his travels to the Philippines, the United States and Pakistan, sometimes using phony passports. Why and how he chose his targets, and how he financed his travels, remain a mystery. Although there is some evidence that he had links to Iraq and to two different Saudi financiers, his clearest connection is to the network around Abdel Rahman.

He calls himself Pakistani "by nationality," Palestinian by choice. That may seem confusing, but there are many rootless young men from the Middle East whose anger at the Western countries, particularly the United States, has become mixed up with their politics and their religion. By Yousef's own account, he was born and grew up in Kuwait in a family of Pakistani and Palestinian heritage. He said he is married and has two daughters, 3 and 1. The youngest was born while he was on the run from U.S. authorities.

He also called himself something else in the April interview, something that U.S. authorities will try to prove when they put him on trial later this year.

"I am," he said matter-of-factly, "an explosives expert." Blauchistan Ties

His real name, Yousef said in the April interview, is Abdul Basit Balochi. But he has become "accustomed" to Ramzi Yousef. He was mysterious about the reason for the name change, just as he is about much of his life.

Similarly, there are various reports about his background, some of them contradictory. According to Yousef, his grandmother -- the Palestinian side of the family -- came from Haifa, and he has other relatives living in Iraq. Pakistani authorities say his father's family traces its origin to Baluchistan, a poverty-stricken area of southern Pakistan and Iran that largely operates outside either government's control.

Traders, smugglers, seamen, professionals and soldiers, the Baluchis have spread out all across the Middle East and Persian Gulf region in search of jobs. This is what Yousef's father did, moving to Kuwait and working as a low-level employee of Kuwait Airlines. At least four of his brothers and two uncles have lived in Pakistan, although there are reports that his wife and two daughters are currently in Iranian Baluchistan. Pakistani investigators said they now believe that many members of Yousef's family are involved in his terrorist activities and have gone underground. Yousef said categorically in April that he did not consider himself to be Kuwaiti, although he grew up and went to government-run schools there.

It was in his home town of Fahaheel -- then populated mainly by exiled Palestinians and guest workers from Syria, Lebanon, Pakistan, India and Bangladesh -- that Yousef apparently first met two other Pakistani Baluchis, Abdul Hakim Murad and Abdul Shakoor. Both would later emerge as partners in his machinations; both have been arrested and have divulged much of what has come to be known so far about Yousef.

Yousef left Kuwait in 1986 to attend the Swansea Institute, a vocational training school in Wales. His enrollment form shows that he registered as Abdul Basit Mahmoud Kareem, not Balochi. He graduated with a degree in electronic engineering in 1989, the year Soviet troops pulled out of Afghanistan, 10 years after their invasion. Invasion of Kuwait

He was back in Kuwait a year later when Iraqi forces invaded the small gulf sheikdom in early August 1990. According to one of his many passports, Yousef left Kuwait City on Aug. 26, heading for Pakistan by road across Iran. There is no evidence he collaborated with the Iraqi occupation regime; instead, he appears to have joined the mass exodus of hundreds of thousands of foreign nationals, including thousands of Pakistanis, who fled Kuwait in the weeks after the invasion.

Yousef's whereabouts in late 1990, during the months when Iraq occupied Kuwait and the United States prepared to lead an allied attack against the Iraqis, is unknown. He next appeared in the Philippines in early 1991, a continent away and with a different mission entirely.

When he arrived in the Philippines, Yousef wanted to make contact with an Islamic militant group called Abu Sayyaf that was waging a guerrilla war for the independence of the southern island of Mindanao, where the Philippines' minority Muslim population is concentrated, according to Edwin Angeles, a former member of the group who is now cooperating with Philippine authorities.

Abu Sayyaf was then a small, little-known movement. According to Angeles, Yousef wanted to meet Abu Sayyaf's leader, Abubakar Janjalani, who was operating from a secret base camp in the southern Philippines. Through an intermediary, Angeles said, he met with Yousef at an apartment in Manila. Yousef, who was then traveling under his real name, arrived with his childhood friend, Murad.

In an interview with The Washington Post, Angeles remembered Yousef as "a very humble man, a good man but also a dangerous man" who said he wanted to use the Philippines as "a launching pad" for a worldwide terrorist campaign.

The meeting with Janjalani did not come off. But in early 1992, Yousef returned for another try and was taken to Janjalani's house in Isabella, the capital of Basilan Island. Angeles, who said he was present at the meeting, said Yousef presented himself as a member of the executive committee of the International Islamic Brigade, an organization that had recruited volunteers for the Afghan resistance. According to Angeles, Yousef also said he had come on behalf of Abdel Rahman, who was offering financial and logistical support for Janjalani's movement. "He wanted to convince Janjalani that the Philippines would be a center of terrorist activities," Angeles said.

It is not known when Yousef first met Abdel Rahman. The Egyptian cleric is known to have repeatedly visited Peshawar, Pakistan -- a center of the former Afghan resistance -- including once in early 1990. Two of Abdel Rahman's sons fought in the Afghan war and spent time in Pakistan.

There is evidence that Yousef had contacts while in the Philippines with a Saudi businessman, Mohammad Jamal Khalifa, who Filipino officials assert was a main financier of Janjalani's Abu Sayyaf.

Angeles said Janjalani and Yousef discussed how they could cooperate on a series of bombings, perhaps even coordinate attacks on the same day. Yousef suggested Janjalani bomb Zamboanga International Airport on Mindanao and that "he would be the one to bomb in the United States," according to Angeles' account.

But Angeles said Yousef never indicated then -- more than a year before the bomb went off at the World Trade Center -- what target he had in mind.

Yousef left the Philippines soon thereafter, bound for Baghdad, investigators have found. According to the indictment in New York, this trip marked the official start of the conspiracy that culminated 10 months later in the World Trade Center bombing. Traveling now on an Iraqi passport, Yousef obtained a visa for Pakistan. Why he traveled on an Iraqi passport, if he is a Pakistani national as he claims, is not clear. He arrived on May 30, 1992, documents show, and spent part of the summer in Peshawar. There, he hooked up with Ahmad Mohammad Ajaj, a Palestinian expelled from Israel who had sought exile in the United States and had come from Texas for training in an Afghan camp. On Sept. 1, 1992, the two men boarded the same Pakistani Airlines flight for the United States, according to investigators. Destination New York

Again traveling on an Iraqi passport, Yousef managed to persuade U.S. immigration authorities at John F. Kennedy airport to allow him into the United States after asking for asylum as an Iraqi dissident. Ajaj was not so lucky. His Swedish passport was found to be fake and his suitcase filled with bomb-making manuals. He was arrested.

Yousef went to stay in an apartment building in Jersey City, where an American-born Iraqi, Abdul Rahman Yasin, and a Palestinian, Mohammad Salameh, also lived. Yasin also was a recent arrival in New York from Baghdad. Yousef and Salameh shared apartments for the next six months in different buildings in Jersey City.

Another bit of intriguing evidence leading back to Baghdad are the more than 40 calls Salameh made to the Iraqi capital in June and July 1992 -- most of them to his uncle, Qadri Abu Bakr. Abu Bakr, who had spent 18 years in an Israeli prison, has been identified as a top official of a now largely inactive Iraqi-sponsored Palestinian group.

During the World Trade Center bombing trial last year, U.S. prosecutors presented evidence that Yousef bought most of the materials used to make the bomb. It was a new kind of explosive device: 1,200 to 1,500 pounds of the chemical fertilizer urea nitrate mixed with ammonium nitrate. FBI bomb analysts say urea nitrate has only been used once before in 73,000 recorded cases of explosions.

The day the bomb went off in the World Trade Center garage, Feb. 26, was the second anniversary of the retreat of Iraqi forces from Kuwait City -- a coincidence that has raised speculation about Iraq's involvement. Hours after the massive explosion, Yousef left on a flight for Pakistan that he had booked two weeks earlier.

Yasin, after an initial interrogation by FBI officials, returned on March 5 to Baghdad where his family now lives. He is still wanted in connection with the bombing.

On March 4, 1994, four defendants -- Salameh, Ajaj, Nidal Ayyad and Mahmud Abouhalima -- were convicted for their roles in the bombing, and on May 24 they were each sentenced to 240 years in prison. Abdel Rahman's trial, on charges of inspiring the World Trade Center bombing and planning others, is still underway; Yousef is expected to come to trial this fall.

Some FBI agents have not ruled out the possibility of Iraqi sponsorship for the bombing. But that theory is discounted by CIA analysts, who have not found any specific proof of Iraqi involvement.

Two days after the World Trade Center detonation, a bomb went off at the Zamboanga airport in the Philippines. Janjalani's group, however, has not claimed responsibility for it.

Back in Pakistan, now on the FBI's 10-Most-Wanted List, Yousef stepped up his militant activities rather than toned them down, Pakistani investigators said.

He stayed mainly in Karachi, hooking up with a small, violent Islamic political party called Sapha-i-Sahaba. The group adheres firmly to Islam's Sunni sect and directs its propaganda against another Muslim denomination, the Shiites, who dominate Iran. Some of its 3,000 to 6,000 members have been charged with murder and causing mayhem on the streets of Karachi and Lahore, mainly in attacks against Shiites.

Within months of the World Trade Center bombing, Yousef was plotting the assassination of Prime Minister Bhutto by bombing her family residence in Karachi, according to statements made to Pakistani police and intelligence officials by Abdul Shakoor, an alleged associate at that time.

Shakoor was arrested Feb. 27 in Peshawar, on Pakistan's border with Afghanistan, carrying grenades, explosives and bomb detonators. Pakistani officials have compiled a nine-page report of Shakoor's statements, a copy of which was obtained by The Washington Post.

According to Shakoor's statement, Shakoor, Yousef and Murad -- all high school friends from Kuwait -- scouted locations where Bhutto might be vulnerable to assassination. Yousef wanted to kill Bhutto because "she is a female and according to Islamic religion, she could not become a prime minister," the police report said.

The plan fell apart in July 1993, when a bomb Yousef was mixing in a Karachi apartment blew up in his face. Between July 23 and Aug. 6, Yousef was treated in two Karachi hospitals, and doctors there have identified him from photographs as the same Ramzi Yousef now being held in New York. Yousef sustained eye damage -- one eye no longer focuses correctly -- and scars on his fingers. In his newspaper interview with Al Hayat, Yousef denied he had been involved in any plot to kill Bhutto and said he received his injuries while helping to train Muslim fighters bound for Bosnia.

Shakoor also implicated Yousef in a bomb blast at a Shiite religious shrine in Mashad, Iran, on June 20, 1994, killing 25 and injuring more than 100 others. Shakoor said he was told by one of Yousef's brothers that Yousef "was responsible for that blast," according to the police report.

Pakistani investigators also believe Yousef received financial support during 1993 and 1994 from another Saudi businessman, Munir Ibrahim Ahmed, who was then living in Karachi. It was Ahmed who paid for Yousef's medical expenses, Pakistani officials said. Ahmed left Pakistan in May 1994, and his present whereabouts are unknown, they said.

Shakoor told Pakistani police that Yousef was a close associate of Ahmed, who made a living in part by importing large quantities of Islamic holy water from Saudi Arabia for sale in Pakistan. Shakoor described Ahmed as "an extreme opponent of Shias, Jews and Americans," according to his interrogation report.

Shakoor also told Pakistani police that while traveling among military training camps inside Afghanistan in 1994 he had met two Arabs -- one from Saudi Arabia and the other from Bahrain -- who had asked him to deliver bomb detonators and a military radio set to Yousef in Karachi.

Yousef also kept going back to the Philippines to work on his plans to blow up American airliners, according to investigators. Angeles, the Abu Sayyaf defector, said it was Yousef who managed on Dec. 11, 1994, while aboard a Tokyo-bound Philippines Airline flight, to put together a bomb that he placed under his own seat. He was accompanied on that flight by Yousef Muhajir, another bomb-making expert, according to Angeles, who called the bombing a "feasibility study" for other similar ones being planned.

After flying from Manila to Cebu, 350 miles to the south, the two men got off, leaving the bomb under seat 26-K. Later, the bomb went off, killing the seat's Japanese occupant and injuring 10 others. But the plane managed to make a safe emergency landing in Okinawa. Plot Against Pope

It was also in late 1994 that Yousef met again with Janjalani in the southern Philippines. According to Angeles, Yousef outlined to Janjalani a plan to assassinate the pope, who was scheduled to visit Manila on Jan. 12.

Angeles said the plot was aborted when, just six days before the pope's arrival, firemen were called to an apartment Yousef and Murad had rented near the papal nuncio's residence, where the pope was to stay. They found no fire, just smoke, but noticed chemical crystals that they thought might be used to make explosives.

In a subsequent raid on the apartment, Filipino police found a road map of the pope's itinerary, a priest's robe, a fragmentation bomb packed into a pipe, a timer made from a digital watch and a pocket calculator.

Angeles said the plan was to use a suicide bomber disguised as a priest to kill the pope and then launch a series of bombings on American airliners over Asia and finally a suicide bomber flying a light plane packed with explosives into the CIA headquarters at Langley.

The next day, police arrested Murad. Yousef had already fled, heading back for Pakistan via Bangkok, investigators said.

With the help of a computer disk they found in the apartment and Murad's confession, U.S. and Filipino authorities were able to put together the details of their plans to blow up 11 American airliners.

Then, on Feb. 7, 1995, the two-year hunt for Yousef ended at a guest house in Islamabad, Pakistan.

Yousef was betrayed by a South African Muslim student, Ishtiaq Parker, an acquaintance living across the street from where Yousef was staying in Islamabad. Parker, whom Yousef was trying to recruit, turned him in, possibly to collect part of the $2 million reward the FBI had offered for information leading to Yousef's capture. He was whisked back to New York for arraignment on the World Trade Center bombing and jailed. Ottaway reported from Washington and New York; Coll reported from Britain, Pakistan and Kuwait. Washington Post correspondent Keith B. Richburg contributed to this report from the Philippines. CAPTION: CHRONOLOGY for Abdul Basit Balochi (Mahmoud Kareem), alias Ramzi Ahmed Yousef. EARLY YEARS

* April 27, 1968: Yousef is born in Kuwait. * 1968-1986: Yousef grows up and is educated through high school in Fahaheel, Kuwait. * 1986: Yousef leaves Kuwait for Britain to attend Swansea Institute in Wales. * 1989: Yousef graduates with an electronic engineering degree from Swansea and returns to Kuwait. * Aug. 26, 1990: Yousef leaves Kuwait City for Pakistan via Iran, three weeks after Iraqi forces invade and begin a seven-month occupation of Kuwait. * Early 1991: Yousef makes his first trip to the Philippines to establish a base of operations for his terrorist activities in the Far East. He makes contact with Islamic militants of the Abu Sayyaf group, including Edwin Angeles, a Filipino who later defects and discloses details of Yousef's plans and activities there.

1992

* Early 1992: Yousef holds a meeting with Abu Sayyaf group leader, Abubakar Janjalani, in his hometown of Isabella, capital of Basilan Island in the Philippines. He says Sheik Omar Abdel Rahman, the Egpytian cleric, sent him to find Janjalani and offer assistance. The two discuss plans to make the Philippines a center for international terrorist operations. * April 12, 1992: Yousef travels from Baghdad to Pakistan via Jordan on an Iraqi passport. * May 30 to Sept. 1 1992: Yousef remains in Pakistan, part of the time in Peshawar, headquarters of Afghan and Arab Islamic groups. * Sept. 1, 1992: Yousef arrives at John F. Kennedy International Airport in New York on an Iraqi passport and seeks asylum citing "political and religious reasons." He is admitted to the U.S., but his Palestinian colleague, Ahmad Mohammad Ajaj, is sent to jail for traveling on a false passport. * Sept. 4, 1992: Yousef begins rooming in three different Jersey City apartments with Mohammad Salameh, a Palestinian with relatives in Baghdad who remains his roommate until the World Trade Center bombing.

1993

* Feb. 26, 1993: A 1,200- to 1,500-pound bomb made out of urea nitrate and ammonium nitrate goes off in the World Trade Center garage, killing six and injuring more than 1,000 others. Yousef leaves New York a few hours later for Karachi.

* Feb, 28, 1993: A bomb goes off at the Zamboanga International Airport in the southern Philippines. The Abu Sayyaf group is suspected but does not claim responsibility for the bombing.

* July 23-Aug. 6, 1993: Yousef is treated at two Karachi hospitals after a bomb he was building goes off prematurely. He sustains injuries to one eye and both hands. Pakistani authorities say the bomb was to be used to assassinate Prime Minister Benazir Bhutto.

1994

* June 20, 1994: A bomb goes off at the Mausoleum of Imam Reza, a Shiite religious cleric, in Mashad, Iran, killing 25 people and injuring more than 100 others.

* Dec. 11, 1994: Yousef allegedly places a bomb on Philippines Airline Flight 434 bound for Tokyo, killing one Japanese passenger and injuring 10 others. The Abu Sayyaf group claims responsibility.

1995

* Jan. 6, 1995: Philippines police arrest Yousef's colleague, Abdul Hakim Murad, after firemen are called to their Manila apartment. Later, authorities find bomb-making manuals and materials, a map of the route Pope John Paul II was to take during a visit to Manila, and computer tapes showing flight schedules of U.S. airlines. Yousef escapes and returns to Pakistan.

* Jan. 12-16, 1995: The pope visits the Philippines without incident.

* Jan 22, 1995: This is the date Yousef and Murad are said to have chosen for blowing up two United Airlines jumbo jets simultaneously as they approached Hong Kong -- one arriving from Los Angeles and the other from Singapore.

* Feb. 7, 1995: Yousef is arrested at a guest house in Islamabad and taken the next day back to New York City to stand trial.

* March 31, 1995: Yousef charged with murder in Manila for his role in the Philippines airlines bombing.

* April 12, 1995: Murad turned over to U.S. authorities in Manila and extradicted to New York. CAPTION: Ramzi Ahmed Yousef's Career

* UNITED STATES -- Charged with leading supporters of radical Egyptian cleric Omar Abdel Rahman in bombing of the World Trade Center, Febraury 26, 1993

* PAKISTAN -- Worked in Karachi with Sapha-i-Sahaba, a small, violent radical Islamic political party with an estimated 3,000 to 6,000 members, beginning in 1993. Investigators believed he planned to assasinate Prime Minister Benazir Bhutto (above); a bomb he was mixing blew up in his hands in July, 1993.

* PHILIPPINES -- Works with Abu Sayyaf, militant Islamic group (below) based in Mindinao beginning in early 1991. Helped plan Febraury 1993 bombing of Zamboanga International Airport in southern Philippines; discussed plans to bomb U.S. airliners, assasinate Pope.

* SAUDI ARABIA -- Received financial support from Saudi businessman Munir Ibrahim Ahmed.

* IRAQ -- Travelled to New York for the Trade Center Bombing on an Iraqi passport; three conspirators had ties to Iraq. * IRAN -- Linked to July 1994 bombing of Shiite shrine in Mashad, in which 25 were killed.

* AFGHANISTAN -- Cooperated with Arab fighters operating inside the country in support of Islamic guerrillas. CAPTION: Ramzi Ahmed Yousef, jailed in New York as the accused bomb builder in the World Trade Center attack, is being investigated in assassination plots and bombings on three continents.