David Truong, the Vietnamese national accused here last week of espionage on behalf of his country, was once a familiar face in Washington's corridors of power. He was a friend, frequent contact and a source of information for several congressmen, senators and their staffs.

He also was acquainted with people at high levels in the State Department and a personal friend of William Colby, the former CIA director.

Last week, on the same day that Truong and U.S. Information Agency employe Ronald Louis Humphrey were arrested or charges of passing secret documents to the communist Vietnamese, FBI agents visited the offices of Rep. Robert E. Drinan (D-Mass) to question one of Drinan's legislative assistants, Elizabeth Bankowski.

She told them she had been helping Truong in his efforts to obtain permanent resident status, but she said the espionage charges took her completely by surprise.The FBI also wanted more information about Truong's activities and friends on the Hill, she said.

"It came as a tremendous shock," said Bankowski, "He knew everyone on the Hill.He certainly was well known to all the (antiwar) cause people." He was, she said, "pretty astute in the way the Hill works."

Now that he is in jail some of the people he has known are coming to his defense, signing affidavits to try to lower his $250,000 bail, and occasionally speaking out on his behalf. Many other who know him are declining comment, and some, who are remembered by his friends as people he dealt with frequently, now say they do not remember him at all.

Rep. Drinan has signed an affidavit on Truong's behalf, to be presented in court today as a partial basis for appeal of his bond. "I know him as a fine person," it says in part, "a man with high ideals and thoroughly honest in all respects.His veracity, character and sense of responsibility are beyond reproach."

According to one of Truong's lawyers, Marvin Miller, affidavits have also been received from well-known Massachusetts Institute of Technology linguist Noam Chomsky, and retired Brig. Gen. Conrad Philos. Chomsky could not be reached for comment and Philos declined comment.

During the last years of the Vietnam war, according to people who knew him well during that period, Truong frequently consulted with antiwar activist groups and made it a point to talk with other people concerned with questions affecting Vietnam.

"Of those who were active in the antiwar movement and on the Hill," recalls Wes Michaelson, a former legislative assistant to Sen. Mark O. Hatfield (R-Ore). "David was one of the most effective and respected individuals by far. He was held in very high regard, even by those who disagreed with him."

Others remember him on a more personal basis. Former CIA director Colby said he knew Truong's parents in Saigon, and saw him on several occasions in the United States. "He's an attractive young man," Colby said. "I feel sorry for him, the way you feel sorry for anyone who's gotten in trouble."

Truong talked on serveral occasions with State Department employes involved with Vietnam peace and diplomatic normalization negotiations, although none claim to have known him well.

Richard Holbrooke, assistant secretary of State for East Asia and Pacific Affairs, told a reporter over the telephone, "I never met Truong. But it looks like I'm practically the only one who didn't." Holbrooke laughed and said, "I guess he knew who was important."