Just after the 1991 Persian Gulf War against Iraq, huge tents were erected in Saudi Arabia near the barracks of U.S. military personnel. Inside, day and night, Saudi imams sent by their government lectured the GIs about Islam and made aggressive pitches to convert them.

Saudi officials had promised that the discussions would touch only on Arab culture. But within months, about 1,000 soldiers, and perhaps as many as 3,000, converted to Islam -- the largest surge of Muslims ever into the U.S. armed forces.

"It was quite aggressive," said David Peterson, then the military's top chaplain in the region. In retrospect, he said, there was reason for concern that foreign clerics had gained influence over the troops, but military officials were slow to grasp the implications, he said.

Twelve years later, with three Muslim employees at the Guantanamo Bay prison accused of security breaches, some U.S. military officials are again wondering whether they have been inattentive to outside influences on the small community of Muslims in the armed forces. But even asking that question is a delicate matter for an institution that has long embraced tolerance of all faiths.

Some military officials believe that the al Qaeda terrorist network is trying to recruit Muslim members of the U.S. armed services and contractors who work with them. Other officers have expressed fears that some Muslim soldiers, sailors and airmen might one day decline to take up arms against fellow Muslims.

Air Force Gen. Ralph Eberhart, head of the U.S. Northern Command, the military's homeland defense unit, said terrorists who try to penetrate the U.S. military by playing on religious or ethnic identities will fail "99.9 percent of the time, with as many 9s as you can add."

Even so, Eberhart said, "there's no doubt in my mind there's an effort [by al Qaeda and other terrorists] to turn our people." Some in the military might be exploitable by terrorists or demagogues because, like other people, they "have sympathies for other causes or nations," he said.

"I'm concerned, and I know others [in the military] are concerned" that foreign extremists might have engineered the security breaches at Guantanamo Bay, the U.S. Navy detention facility in Cuba where about 660 alleged al Qaeda and Taliban fighters are held, he said.

Military sociologist Charles Moskos is traveling to Iraq this month to poll troops about morale issues. He plans to ask whether Muslim soldiers seem to have their hearts in fighting fellow Muslims, and whether the troops trust Muslims in their ranks.

"I'll ask, 'How do you feel about having a Muslim in your tent?' " Moskos said.

A black Christian Army chaplain based in this country said some of her fellow soldiers feel "tension" with Muslims in their units, many of whom are also black. "They say, . . . 'Can we really trust them?' "

Allegiance Assumed

Despite these concerns, U.S. officials say they have seen almost no evidence of hesitancy, much less disloyalty, among the 5,000 to 10,000 Muslims in uniform, and believe only a tiny number would ever be vulnerable to manipulation by foreign extremists. In the Marines, for example, only three Muslims have switched military assignments or requested conscientious objector status since the Sept. 11, 2001, attacks, officials said.

Some critics of government terrorism policy say the Pentagon is so devoted to promoting religious brotherhood in its ranks that it fails to discern traces of anti-American sentiment among Muslim troops. "The military has a style of political correctness that says, 'We're not in the business of judging anyone's religion,' " said Thor Ronay, a terrorism researcher at the conservative Center for Security Policy.

Questions about Muslim personnel's allegiances have been raised inside the military by the arrests of the trio at Guantanamo Bay. Each was found with secret documents that officials said they were not authorized to have.

One, Army Capt. James Yee, a chaplain who ministered to the prisoners there, had expressed feelings of identification with the captives and may have shifted his allegiance to them, officials have said. Yee converted to Islam after he came in contact with Saudi clerics during an Army tour in that country in 1991.

Another of the accused men, Air Force Senior Airman Ahmad I. Halabi, an Arabic translator, had intense misgivings about the prison and U.S. foreign policy, according to court documents. The third, civilian translator Ahmed F. Mehalba, was arrested at Boston's Logan International Airport as he returned from a trip to Egypt with classified information on at least one computer disc, the government has contended.

Investigators are seeking to determine whether the three, or any pair of them, were working together, and whether they were communicating with governments, terrorist groups or others who might have use for the information they carried. The probe is one of the first into the activities of Muslim service members since the mass conversions in 1991.

Despite their initial upset that Saudi officials had misled them about the tent lectures, U.S. officers did not end the gatherings, in keeping with the military's bedrock principle of accommodating all faiths, Peterson said.

One of the Saudi-trained imams who organized the effort, Bilal Philips, told London's al-Majallah magazine in August that the tent meetings were run by "a special team whose members spoke fluent English," including some experienced in broadcasting and psychology. The well-financed team paid for the converts' pilgrimages to Islam's holy cities, and upon their return home, arranged follow-up visits by Muslim clerics in the United States, said Philips, a Jamaican-born convert.

U.S. officials never kept records on how many GIs converted, but the rapid rise in the Muslim population caught senior officers' attention.

"There was a concern about the ability of the Muslim community to take up arms against fellow Muslims," recalled Herman Keizer, then an Army colonel who headed the military's chaplains board. "There was also concern about what influence events in the Middle East could have on Muslims in the military."

It became clear that Philips was not a friend to U.S. policy. "The clash of civilizations is a reality," he said in the interview. "Western culture led by the United States is an enemy of Islam." With his encouragement, some of his U.S. military converts trained Islamic fighters in Bosnia in the 1990s and were later investigated by the FBI in terrorism probes in this country, he added.

By the early 1990s, the Pentagon was working closely with U.S. Muslim activists to hire Islamic chaplains to minister to Philips's new converts and their co-religionists. One architect of this initiative was Abdurahman Alamoudi, who was indicted Oct. 23 on money-laundering charges for allegedly taking hundreds of thousands of dollars from Libya, which is designated by U.S. officials as a state sponsor of terrorism.

Military Admits Lapses

In hindsight, military officials "might have been more suspicious" of the conversion efforts and the key role in the chaplaincy campaign played by Alamoudi, given his many public statements of support for foreign groups designated as terrorist organizations, Keizer said. "I don't think the military had a sense of some of the global issues," he said.

Officials also have acknowledged inattention to security issues posed by linguists hired in the war on terrorism. The scarcity of Arabic translators has led military officials to cut corners in security checks of them, officials said. Both Halabi and Mehalba had received quick "interim" clearances.

The Mehalba and Halabi cases are "the results of that," Charles Abell, a top Pentagon personnel official, told a Senate hearing on Oct. 14. "We've found a couple who were not as trustworthy as we had hoped."

Kevin Hendzel, a spokesman for the American Translators Association who works closely with the military, said officers often are so desperate for Arabic linguists they employ them despite fears they are al Qaeda plants. "Al Qaeda knows we're short of linguists, so it's a natural pipeline for infiltration by them," he said.

But Marine Sgt. Jamal Baadani said many such security fears are baseless. The founder of a group called the Association of Patriotic Arab Americans in the Military, Baadani said many Muslims are performing sensitive jobs in the war on terrorism. "This is our country," he said during a break from his classified combat job in the Middle East.

He said he resents implications that Muslim soldiers may be disloyal, an insult he said is compounded by criticism he receives from other Muslims. "I've been called a traitor and an Uncle Tom by fellow Muslims" for serving in the military, he said.

Marine Sgt. Mike Gatto, a practicing Muslim, said he is unaware of any Muslim personnel opposed to fighting in Iraq. "To the contrary, I knew several who went willingly," he said. "Saddam needed to go, and many Muslims will say the same thing when pressed, Marine or not."

But a few cases of disloyalty have emerged in recent years. In 2000 Ali Mohamed -- a highly placed al Qaeda operative who had infiltrated the U.S. military and became a sergeant in the Army Special Forces -- pleaded guilty to conspiracy in connection with the 1998 bombings of two U.S. embassies in East Africa.

Last month, Jeffrey Leon Battle, a former Army reservist from Portland, Ore., pleaded guilty to conspiracy to levy war against the United States after trying for months to enter Afghanistan to fight U.S. forces. U.S. prosecutors said he enlisted in the reserves "to receive military training to use against America."

Last March, as his unit prepared to enter Iraq from Kuwait, Army Sgt. Hasan Akbar killed two of his commanding officers in a grenade attack as they slept. Relatives said Akbar, a Muslim convert recently disciplined for insubordination, had sensed persecution as a Muslim. He had avoided serving in the first Gulf War because it conflicted with his faith, said relative Quran Bilal.

Radical forces in the Muslim community at times have impinged on Muslims in the military, which happened when U.S. forces prepared to invade Afghanistan in 2001. A Muslim chaplain in the Army asked a leading Islamic scholar, Taha Jabir Alwani, president of a Virginia institute that trains Islamic military chaplains, for a fatwa, or religious decree, on whether Muslims could fight fellow Muslims. A "no" answer would have created a crisis.

To write his fatwa, Alwani consulted, among others, Yusuf Qaradawi, a popular cleric in Qatar who has been banned from the United States for his strong support for suicide bombings against Israeli civilians.

The fatwa ultimately hedged. While saying Muslims could fight for the United States in Afghanistan, it stressed that Muslim GIs also have the option of refusing to fight. The military does not allow soldiers to choose wars in which they will participate.

Mahdi Bray, a Muslim activist in Virginia, said the fatwa was ambiguously worded to allow Muslims to serve while also granting ground to influential hard-line Muslims who oppose the U.S. war on terrorism.

Despite its artful wording, "it created an uproar in the Muslim community" because some hard-liners took it as a pro-U.S.-military stand, Bray said. "It pleased no one" in the Muslim community.

Senior Airman Ahmad I. Halabi is one of three Guantanamo Bay staff under investigation. Ahmed F. Mehalba, a civilian translator, was arrested carrying classified information. Army Capt. James Yee, a chaplain, converted to Islam while serving in Saudi Arabia.