Complex political and legal maneuvering here and in Washington has placed a major suspected cocaine kingpin almost within the grasp of U.S. officials and blocked the release from federal prison of Michael Vernon Townley, the Iowa-born Chilean secret policeman who confessed to the 1976 assassination in Washington of former Chilean ambassador Orlando Letelier and a coworker.

Townley was quietly granted parole last month and was to have been freed May 6, after serving just over five years of a sentence of 40 months to 10 years. That term was specified in his agreement to testify against Chilean officials and Cuban exile militants charged with helping him kill Letelier in 1976.

Less than 24 hours before Townley's scheduled release from a U.S. prison, Argentina presented a request for his extradition on charges that he murdered another prominent Chilean, Gen. Carlos Prats, and Prats' wife in Buenos Aires. Townley, whose whereabouts are confidential because of his status as a protected witness, was then placed under preventive detention pending extradition hearings.

Townley's attorney, Seymour Glanzer, said in Washington that the U.S. cooperation in the extradition of Townley is a breach of the witness protection agreement. "They wouldn't turn him over to Chile, would they?" Glanzer said. "But they're in the process of turning him over to Argentina."

In Argentina, the request for Townley was immediately linked by press accounts to the U.S. request a week later that Argentina extradite Bolivian ex-interior minister Luis Arce Gomez.

Arce Gomez, who was living here under a grant of political asylum and considered to have close ties to the Argentine military, was indicted by a Miami grand jury on charges of working out of his Bolivian government post to direct a conspiracy with 17 other persons to smuggle hundreds of pounds of cocaine into the United States. Argentine police placed Arce Gomez under preventive detention Monday.

The Buenos Aires newspaper La Nacion said the two extraditions, if granted, would be "a curious case of simultaneity."

Under provisions of a 1972 extradition agreement between Argentina and the United States, Arce Gomez and Townley face judicial clocks ticking at about the same rates. The respective governments have 45 days from the date of arrest to back up their extradition requests with evidence showing "probable cause" of the two men's alleged guilt.

Townley, appearing at a closed preliminary hearing today in U.S. District Court in Alexandria to begin the extradition process, was denied release on bail.

U.S. and Argentine judicial officials said they know of no connection between the Townley and Arce Gomez cases. A senior U.S. diplomat here said, "The fact is these two cases came together at the same time. That's the only connection, in our minds at least. The Argentines may think differently, but I doubt it."

In Washington, Art Brill, deputy director of public affairs of the Justice Department, said, "The two cases were a coincidence, but you could call it a cooperative law enforcement effort." He said the Justice Department would handle the Argentine request in Washington and the Argentine judicial officials would represent the United States in proceedings in Buenos Aires.

A U.S. investigator in Washington close to the Letelier investigation said he had been told by an Argentine intelligence official that Argentina will "wait and see what happens with Townley before acting to turn over Arce."

The U.S. official said he got a call from the Argentine officer, a long-time friend, four days after Townley's arrest on preventive detention. "Everybody knows what will happen," he quoted the officer as saying. "If we don't get Townley, you don't get Arce Gomez. Everybody understands that."

The officer said in the call that the Argentine prosecutor, who has been gathering evidence with U.S. help for several years on Townley's alleged role in the 1974 car bombing that killed Prats, waited until the last minute to file extradition papers to make the timing of the two cases run "neck and neck."

Argentine officials investigating the Prats case visited the United States several times in 1980 and 1981 to go over evidence that U.S. investigators had presented in the Letelier case that allegedly linked Townley to the Prats murders. That evidence includes a passport Townley used and other documents that show he was in Argentina at the time Prats was killed.

U.S. investigators said they also provided the Argentines information with which they could show similarity between the type and placement of the car bombs used in both cases.

According to the federal investigator in Washington who talked to the Argentine intelligence officer, the Argentines also have the confession of a Chilean, Enrique Arancibia, who allegedly worked with Townley in the Prats murders.