The Panamanian leader, Gen. Manuel Antonio Noriega, has obtained payoffs and hidden profits of millions of dollars for himself and a group of Panamanian military and civilian associates by selling government services and influence, according to a former top Noriega political adviser and aide, Jose I. Blandon.

The services sold by Noriega and his associates include passports, visas, airport landing rights and merchant marine identification cards for crewmen aboard Panamanian-registered vessels, said Blandon, who for several months late last year was Noriega's secret emissary to the Reagan administration.

In more than eight hours of interviews last weekend, Blandon charged that Noriega had used his 4 1/2-year reign as military commander-in-chief and de facto ruler of Panama to convert the government into a "criminal enterprise."

After what were described as repeated death threats, Blandon and his family on Sunday were placed under 24-hour guard by the U.S. Marshals Service, according to informed sources. Noriega fired Blandon last month from his job as Panama's consul general in New York.

On Thursday, Blandon testified for about five hours before a federal grand jury in Miami that is investigating Noriega's alleged ties to the multibillion-dollar Latin American drug trade. Federal prosecutors are expected to seek an indictment soon, possibly this week, sources said.

Noriega has repeatedly denied any involvement in drug trafficking or other corrupt activities. A Noriega spokesman recently said Blandon's allegations are "ridiculous."

The spokesman added that Blandon was not part of Noriega's inner circle and did not have access to the information he says he has.

In this weekend's interviews, Blandon characterized Noriega's alleged involvement in drug trafficking as only one component of a systematic pattern of corruption.

Blandon compared Noriega to Ferdinand E. Marcos of the Philippines, the late Shah Mohammad Reza Pahlavi of Iran and the late Anastasio Somoza of Nicaragua. "They were corrupt," Blandon said. "Noriega is a criminal . . . . He has more lucrative businesses than Somoza."

Blandon said that Noriega and his associates derive profits and commissions from hidden interests they allegedly have in Panamanian businesses. In particular, Blandon said, they are active with firms that operate in Panama's Colon free zone, a duty-free trading center through which millions of dollars in high-technology goods and other products are moved.

Blandon alleged that Noriega has a hidden interest in a company that last year was hired by Aeroflot, the Soviet airline, to act as its agent in Panama. He said he has been told that Noriega has a 15 percent interest in the Panamanian firm and is expected to make millions of dollars from the Aeroflot deal.

Blandon provided a copy of what he said was the agreement, dated Aug. 6, 1987, between the Panamanian firm and Aeroflot. He identified the person signing the purported document for the Panamanian firm as a close Noriega associate who allegedly was placed in charge of the firm to safeguard Noriega's interest.

Blandon, 44, said he has known Noriega since 1971 when Noriega was the military chief of a key Panamanian province where Blandon worked as a land reform official.

Blandon said he later became a political adviser to Brig. Gen. Omar Torrijos, the charismatic Panamanian leader who negotiated the Panama Canal treaties with the United States. Torrijos died in a plane crash in 1981. Blandon said he remained as a top political adviser after Noriega became military commander-in-chief in August 1983.

U.S. officials confirmed yesterday that Blandon was close to Noriega and they said they have found Blandon to be credible.

"He knows the way Noriega thinks," said one State Department official. "I find him credible."

The official said that reports from the U.S. Embassy in Panama indicate that Noriega and his aides are "very concerned about what Blandon might say."

Another U.S. official familiar with Blandon's statements to federal prosecutors in Miami said that his information was helpful to the investigators. "{The prosecutors} had a good case," the official said.

"{Blandon} added the spice."

"He made what {the prosecutors} had fit into perspective and he added irrefutable corroboration," the official added.

Blandon said that he is now speaking out because Noriega is hopelessly corrupt and must relinquish power if Panama is ever going to have a democracy and live in harmony with the United States.

He said Noriega has subverted Torrijos' plan to reduce the role of the military in Panama's government so that civilian leaders would be entrenched by the time the U.S. relinquishes sovereignty over the Panama Canal in the year 2000.

Blandon said Noriega has again made the military the dominant force in Panamanian politics and government.

Noriega, who was the head of Panamanian military intelligence, known as the G-2, for 13 years, accomplished this by placing a coterie of his close G-2 aides in key positions that gave him control over the police, immigration, the airports, harbors, and the issuance of passports and visas.

Simultaneously, Blandon said, Noriega put together a network of civilian business associates who became his alleged links to the drug trade, private commercial firms and a wide array of other ventures.

However, Noriega's power has been sharply challenged following riots against his rule last summer, mobilizing unprecedented internal opposition against him. The Reagan administration has stepped up efforts to push Noriega out of office, and Congress has voted to cut off virtually all U.S. aid to Panama.

Blandon said that last fall he received Noriega's approval to serve as an intermediary in attempts to resolve differences with the Reagan administration and the Panamanian political opposition.

However, Noriega abruptly ordered Blandon to halt his efforts late last year, fired him last month as consul and branded him a traitor.

Noriega has a fixation with money and power, and plays enemies against each other in regional and international disputes, according to Blandon. For example, one day he fed sensitive strategic and tactical intelligence on the El Salvador army to Cuba, which backs the leftist insurgency there, and the next day met and shared information with Salvadoran army officers, Blandon said.

He said when he asked Noriega why he did this, Noriega replied, "We have to keep the equilibrium."

Blandon said that Noriega provides sensitive information obtained from the CIA to Cuban intelligence. "The only thing he protects is the names of CIA officers in the U.S. Embassy," Blandon said, because Noriega wants to maintain his channels to the agency, with whom he has a long history of cooperation.

As an example of one of Noriega's money-making schemes, Blandon said Panama sells visas for $4,000 apiece to Cubans hoping to emigrate to the United States. The Cubans use the visas, for which the official fee is only $10, to enter Panama and then travel to the United States. Over the last several years, Blandon said, 20,000 such visas have been sold -- which would have added up to $80 million in tainted income from this operation.

Cuban President Fidel Castro receives numerous favors from Noriega, according to Blandon. "Fidel needs Noriega," Blandon said. "He knows he's not a communist. He's a businessman."

Noriega, for example, allows Castro to funnel arms through Panama for the guerrilla movement in Columbia called M-19, to transfer shrimp from Cuban's fishing fleet through Panama to the United States, and to use companies in Panama to obtain advanced technology from the United States, Blandon said.

Blandon also said that Noriega has ties to the organization of political extremist Lyndon H. LaRouche Jr. Blandon said the general had paid money to the LaRouche group for assistance. But he said the LaRouche group views the money as donations, not payments in exchange for its support.

LaRouche and his group have publicly praised Noriega and denounced his critics as drug dealers. In an interview last year, LaRouche described Noriega as a "brilliant man" and "one of the best anti-drug fighters on the continent."

Staff writer John Mintz and staff researcher Melissa Mathis contributed to this report.