He is the confessed hit man in the violent bombing assassination of former Chilean Ambassador Orlando Letelier, a man described by a friend as a "romantic counter-revolutionary." An American youth, born in Waterloo, Iowa, he joined the clandestine world of a foreign country's secret police, giving it an almost fanatical commitment.

He now has been linked, through his own court testimony or the statements of investigators, to assassination plots in four countries to "eliminate" the most prominent of exile leaders opposing the current Chilean military dictator, Augusto Pinochet.

At the same time, people who have known him for years recall his days as a youthful church leader in Chile, a talented boy who seemed destined, if not for greatness, at least for a successful upper middle-class life.

Still, as the tangled life of Michael Vernon Townley unfolds in a U.S. court here, he seems like a half-finished painting: The broad outlines of his life are clear, but the finished portrait is still a mystery.

Part soldier of fortune for the Chilean secret police, part anti-Communist fanatic whose Nietzschean ethics condone murder, part duty-bound follower of orders who still refers to the Chilean secret police as "my service," part concerned family man -- all phrases describe Townley.

Townley's appearance last week as the chief U.S. witness in the trial of three anti-Castro Cuban exiles charged in connection with the Letelier murder has raised many quetions:

Is he or was he ever an agent for the CIA? Was he a double agent, a "mole" planted by the CIA in the Chilean secret police, once known as DINA? Is he a pawn in a scheme to extricate Pinochet from a crisis that has threatened to topple his regime? And what of the larger political implications of the as sassination along Washington's Embassy Row in September, 1976 -- the most brazen act of international terrorism ever carried out here.

A dozen years ago, one might have felt comfortable sitting next to Townley at a church service. Last week, however, U.S. District Court Judge Barrington D. Parker pointedly observed that such would not now be the case.

Parker, a jury of seven women and five men and a transfixed, packed courtroom audience had heard the 36-year-old DINA agent describe in excruciating detail how he had carried out the assassination on the orders of DINA.

From Townley's testimony emerges the figure of a mild-mannered, well-spoken electronics technician whose specialty happens to be remote control bombs to assassinate Pinochet's exiled political opponents, a man who travels with his wife (also a DINA agent) on his missions of death and sends souvenirs to his children.

A variety of persons who have spoken with him since his arrest in the Letelier case say that he also continues to consider himself a loyal DINA officer and follower of Pinochet.

A friend who knew Townley and his family in the early 1960s said he has trouble conceiving of today's Townley as the same person he first met in a Methodist church youth group in Chile.

"He demonstrated to me the type of characteristics you associate with a high-achiever, a very personable young man. I would have expected him to have become a lawyer, perhaps an electronics engineer," the friend said.

Townley is the biggest enigma in the puzzling framework of intrigue surrounding the Sept. 21, 1976, assassination of Letelier and Ronni K. Moffitt, a colleague of his at the Institute for Policy Studies. His willingness to describe the crime he committed and implicate the three Cubans while refusing to answer a question about his activities with the Chilean secret police has become the principal controversy in the Letelier trial, as it heads into its third week. Judge Parker is expected to rule today whether Townley can invoke the 5th Amendment right against self-incrimination for actions in Chile.

Defense attorneys for the three Cubans contend Townley is not a loyal DINA agent at all, but a CIA "mole" who infiltrated DINA and carried out the Letelier assassination as a CIA operation and then framed the Cubans. The attorneys have not supplied any evidence to support this allegation.

The mystery about Townley begins with that fact that he was born in Waterloo, Iowa. How did he turn up 30 years later as a trusted secret police electronics expert in Chile?

Townley was on the witness stand last week because last April the U.S. government identified him as a suspect in the murder and asked -- using considerable diplomatic arm-twisting -- the Chilean government to expel him.

Inexplicably -- if Townley really was a Chilean agent and acting on secret police orders in killing Letelier -- the Chilean authorities arrested Townley, and turned him over in handcuffs to FBI agents aboard a jet flight to the United States.

From interviews with people in Chile and the U.S. who knew Townley -- some as friends, some as comrades in militant right-wing groups, and one who was a fellow DINA agent -- a complex and contradictory picture emerges.

Townley's acquaintances had little negative to say about the man. "Likeable," "genius," "sincere," "gave the impression of a Mormon missionary," "harsh and cold" were some of the descriptions heard.

Townley's youth was conventional though troubled. He was 14 when his father, Vernon Townley, became head of Ford Motor Co. operations in Chile in 1957 and moved his family to Santiago.

Active in the American community's Methodist Church youth group, but not particularly religious, Michael as a teen-ager was considered to be sociable and a natural leader.

The Townleys' life style in Chile reflected their affluence and he was sent to the exclusive St. George's High School, run by the American Holy Cross order. Though obviously intelligent, he had trouble with Spanish at first and dropped out without a high school diploma.

A counselor described Townley's home life as tense and unhappy under the domination of his father. Before he was 20, in defiance of his parents, Townley married Mariana Callejas, a twice-divorced, unpublished writer 10 years his senior. She had two small children. Townley, who became a stock salesman, began to consider himself as much Chilean as American.

For a number of years in Chile he earned a comfortable living as a successful salesman of mutual fund stocks from the later controversial Bernie Cornfeld firm, Investors Overseas Services. Townley had a numbered Swiss bank account.

The first sign of Townley's later double life appeared after he moved his family to Miami in 1967. There the stock salesman's conservative suits were replaced by jeans and boots as he began to work as an auto mechanic in Miami's Little Havana.

His friends were anti-Castro exiles and beneath the blue-collar exterior, his knowledge of electronics grew increasingly sophisticated.

To his neighbors, he was apolitical. At a time when the leftist government of then-president Salvador Allende was elected in Chile in 1970 and many Chilean rightists emigrated to flee what was seen as a coming social revolution, Townley moved his family back to Chile.

Before he left, Townley testified last week, he contacted the CIA office in Miami and offered his services in Chile. The CIA, while once seeking to use Townley in an "operational capacity," says its records do not reflect whether it ever used Townley as an agent. Townley said he never worked for the CIA.

Once in Chile, Townley won his stripes as an anti-marxist "freedom fighter," when he built a clandestine mobile radio station for anti-Allende propaganda by mounting a powerful transmitter in the rear of his Austin Mini car.

During a 1972 truckers' strike against the government, during which Allende put radio stations under state control, Townley's "Radio Liberation" broadcast virulent antigovernment messages and songs -- some written by Mariana Townley. He evaded the efforts by military intelligence assigned by Allende to locate the illegal transmitter.

Townley was recruited by the most violence-prone of the opposition groups, Fatherland and Liberty, for other operations, including one that resulted in a man's death. Townley was identified as having participated in that operation and for the first time, in June 1973, was labeled a CIA agent by a leftist newspaper. In fact, Townley bragged to friends at the time that he had CIA contacts.

He fled Chile by crossing the Andes Mountains on foot. Within a few months the Chilean military answered the pleas of the right-wing groups and overthrew the Allende government in a bloody coup on Sept. 11, 1973.

Townley spent several months back in the U.S. and then was recruited into DINA after his return to Chile by L. Col. Pedro Espinoza, the same military intelligence officer who unsuccessfully had searched for Townley's clandestine transmitter in October 1972.

According to informed sources, the head of DINA, then Col. Juan Manuel Contreras Sepulveda, provided the Townleys with a sprawling, rundown mansion in the Locurro district of Santiago. The sources said Townley installed a high-powered VHF radio transmitter in the house, using it to keep in contact with his DINA subordinates working around the city in cars.

From his recruitment in 1974 to his expulsion from Chile last year, Townley has linked himself or has been linked by various investigators to a chilling list of assassinations as well as abortive attempts to eliminate exile opponents of Pinochet's government.

His modus operandi was simple: Use car bombs set off by remote control equipment that he built and modified himself. The toll: Four dead in car bombings, two seriously wounded by gun shots. Two exile leaders escaped unhurt.

Investigators have linked Townley to the 1974 car bombing that killed exiled Gen. Carlos Prats and his wife in Buenos Aires and to the pistol attack on Christian Democratic leader Bernardo Leighton and his wife in Rome in 1975. Leighton, an exiled proponent of a united leftist Christian Democratic front against Pinochet, recovered from wounds but his wife is partly paralyzed.

Townley testified last week that he also undertook a mission to Mexico in 1975 with bomb equipment intended to kill Socialist leader Carlos Altamirano and Communist leader Volodia Teitelboim. But he said he arrived too late.

According to terms of a plea-bar-gaining agreement between Townley and the Justice Department, he is not required to testify about crimes other than those committed within the United States or against American citizens. He eventually will be sentenced to a 3 1/2-to-10-year sentence for his role in the Letelier killing.

One investigator last year gave this explanation for Townley's unwillingness to go beyond the bare bones of his DINA role: Townley intends to return to his adopted country after serving his sentence.

"Townley wants to get the point across that he and his wife aren't talking about other cases, and that he isn't talking about matters of (Chilean) national security. He was turned over by the Chilean government and told to cooperate and he is cooperating with information, but only for the matter he was turned over for (the Letelier killing). All he wants to do is to be able to return to Chile some day," the investigative source said.

That reasoning shed some light on Townley's continual use of "my service" in his testimony when he is refering to DINA.

Townley and his family, including his father, now a banking executive in the Miami area, his mother, sisters and brother, have been given protection under the U.S. witness protection program. Michael Townley, under arrest, and his wife are together somewhere in the Washington area, but their whereabouts have been kept secret. Townley is allowed to make telephone calls and he does frequently, including calls to journalists in Chile and Europe.

In a recent call to a friend, Townley stressed his loyalty to Pinochet, referring to him as "his excellency." He was quoted as saying, "Pinochet didn't know anything about (the Letelier murder) and I can prove it."

Nonetheless, he said he was hurt by Pinochet's virtual disavowal of any knowledge of him. "That hurts because I have had personal commendations from his excellency, so there's no way he can say he doesn't know me..;" the friend quoted Townley as saying.

Mariana Townley, who has admitted frequently telling false stories to jour-nalists about her husband to protect him before he was expelled, says she is furious at what she calls the Chilean government's "betrayal" of her husband. In recent interviews she has directly acucsed Pinochet of giving the order to kill Letelier.

In one interview with The Washington Post, she said her husband had "grave doubts" about the mission to kill Letelier, but "was not a person who disobeyed orders."

She wrote once "My husband was always more afraid of confessing fear than of whatever provoked his fear."