Michael Vernon Townley, a soft-spoken, intense and articulate 35-year-old man who has made Chile his home for the past 20 years already is starting to be known in some circles as the "John Dean" of the Letelier affair.

He is an unlikely figure to be found in his current role - as the heavily guarded informant who has calmly told FBI agents and prosecutors how he followed orders to plant an explosive whose blast left its intended victim so mangled that hardened investigators became sick at the scene of the crime.

As he is described by people who know him. Townley is a skilled electronic technician capable of assembling devices to detonate bombs by remote control. He had been active in commando raids against the late Chilean President Salvador Allende, whose Marxist regime was toppled in a military coup by the current Chilean president, Gen. Augusto Pinochet.

Townley, an American who grew up in Chile where his father headed a large U.S. automobile operation, had become a familiar sight to Americans there by the early 1970s. He was known as a political activist who was suspected of participating in military activities of Patria y Libertad, a rightwing Chilean party.

Although he had been charged with murder for his alleged participation in a Conception raid in which a night watchman was killed, the charges were dropped when Pinochet came to power in late 1973 and Townley became an agent of DINA, the Chilean secret police agency.

Townley was expelled from Chile in early April after the U.S. put intense pressure on the country to turn him over. In the U.S., his attorneys, Seymour Glanzer and Barry W. Levine, struck up a deal by which he would enter a guilty plea to one count of conspiracy to murder Letelier and would in return cooperate in the Letelier investigation.

As a part of the deal, Townley will only have to cooperate with and provide information to U.S. authorities on his role in the Letelier murder. He reportedly has additional information about terrorist activities in other countries, but is not required to give that information to the U.S., sources have said.

As was John Dean in the Watergate affair, Townley was, by his own account, directly involved in the execution of crimes and has decided to testify against his close associates. And, as in Watergate, Townley could, as did Dean, play a central role in questioning the activities of a country's highest government officials.