Michael Vernon Townley, expelled Saturday from Chile, was arraigned here yesterday as a material witness in connection with the 1976 murder in Washington of former Chilean diplomat Orlando Letelier, the FBI said.

An FBI spokesman said Townley, 35 is to appear this morning before Chief Justice William B. Bryant of the U.S. District Court for the District of Columbia. Bryant issued the material witness warrant under which Townley was taken into custody, the spokesman said.

According to the FBI, Townley arrived yesterday morning at Baltimore Washington International Airport in the company of FBI agents and was taken by them to Fort Meade, Md. The FBI said Townley was "in federal custody" last night "in the Washington area."

The arraignment took place before a U.S. magistrate in Prince George's County, the FBI said. Further details were not immediately available.

Townley was ordered expelled from Chile on the ground that he had violated regulations concerning the residence there of foreigners.

Townley has been identified from a photograph as one of two men who traveled to the United States a month before the killing. He also has been linked by sources to the Chilean secret police, and described as an activist in a militant rightist organization during the leftist government of Salvador Allende, Letelier was an official in the Allende government.

Townley reportedly refused to answer any of the 53 questions put to him during a session in a Chilean court on March 25 that was supervised by a Justice Department investigator.