The top aide to Rep. Daniel J. Flood (D-Pa.) is said to have told friends in 1976 that his $37,000-a-year job was worth $100,000.

A witness at last fall's bribery trial of Stephen B. Elko here said the Flood aide was angry because he was being forced out of his job in order to head off a House investigation. The probe centered on his involvement in a kickback scheme to channel federal funds to a chain of California trade schools.

"For years I have been doing all the dirty work, and the old man has been getting all the gravy, and now it is my turn. I'm not going to be forced out," Louise Fleming, wife of a close Eklko friend, quoted the Flood aide as saying.

Elko left the congressman's payroll at the end of June, 1976. He was indicted on federal bribery charges stemming from an earlier Senate investigation last June and was convicted last fall.

He has been cooperating with federal prosecutors since December, and is reported to have described several schemes in which Flood allegedly took more than $100,000 over the years in return of his influence as chairman of a powerful House Appropriations subcommittee.

Flood has denied the charges.

The Elko trial record in Los Angeles includes a bizzare collection of testimony about the cash in envelopes passed to the Flood aide by two key witnesses.Deryl Fleming and William Fred Peters, to clear the way for federal funding of Peter's West Coast Trade Schools.

Peters was convicted earlier for his role.

For instance, the alleged consipirators talk of the need for "five suit of long underwear" - code words for $5,000 in $100-bills - to help Peters' schools get accredited. A "suit of short underwear" was a single $100 bill.

"There is testimony, too, that some $10,000 of the bribe money was stashed in the rafters of the basement of Fleming's house for several months. He didn't keep it in the bank, he said, because he feared his wife would spend it.

When investigators began to close in during 1975 the trio began discussing ways to "stonewall" it by coordinating their stories according to testimony. They even used tapes of previous sessions with investigators at one point to make sure their versions of events coincided.

There are also signs in the trial record that Flood would become a target of federal investigators. First Peters, then Fleming and finally Elko have become government witnesses. Now, under grants of immunity, they are providing testimony implicating Flood in the trade school kickback scheme, the court record shows.

As early as August, 1975, when he was arrested on a passport violation, Peters offered to implicate a congressman in exchange for immunity. Prosecutors refused at the time, and he was later convicted for having bribed Elko in the scheme.

But last May, in the face of further charges, he was given immunity. About the same time, Fleming also became a government witness.

Their testimony led to indictment of Elko and his girlfriend, Patricia Brislin, in June, just a few days before the statute of limitations ran out.

An FBI agent's summaries of interviews with Peters and Fleming show that they implicated Flood as well.

In his May 11 interview, Peters said it was his understanding that Flood "would ultimately receive the money" he had paid to Fleming and Elko. Peters estimated that between 1972 and 1973 "he paid Congressman Flood approximately $50,000 through Fleming and Elko," the FBI statement said.

Fleming's May 23 interview included a statement that he gave Flood $1,000 in cash in Elko's presence in 1972 for aid for Peter's trade schools.

Fleming also stated according to the FBI statement, that Elko said, "Flood's a greedy man and he's got to be taken care of."

Though neither of the FBI statements was introduced into evidence at the trial, both were used by the defense as a basis for cross-examination, and are available in the court record.

Elko was indicted almost a year after he signed under pressure as Flood's administrative assistant.

The trial reference to his angry statement about being forced out did not identify the "old man" whom he said was "getting all the gravy." Fleming's statement to the FBI, however, said that Elko referred to Flood as the "old man."

Trial prosecutor David W. Hinden, an assistant U.S. attorney in Los Angeles, did not ask witness Louise Fleming how Elko's job was worth $100,000.

Elko did not have the witness stand. Flood did, but was not questioned about the allegations Peters and Fleming made to the FBI.

Sourecs familiar with the investigation have told The Washington Post that prosecutors are checking the possibility that Flood and a close friend, Elko's former attorney, John L. Ingoldsby Jr., tried to buy the aide's silence by promising to provide support payments and legal fees after he resigned.

Ingoldsby said in a recent interview that he did arrange for the payment of legal fees for Elko and Brislin. He denied any criminal intent.

Elko did not cooperate with investigators at first, even after his conviction last fall. He refused to answer questions before grand juries in Washington and Philadelphia in early November, according to sources familiar with the investigation.

He finally began to talk and implicate Flood in December after being threatened with "use immunity," which compels testimony, the sources said.

The Philadelphia grand jury wanted to question Elko about his role in helping obtain a $14.5 million federal grant for a Philadelphia hospital. He reportedly has implicated both Flood and Rep. Joshua Eilberg (D-Pa.) in connection with that transaction.

The Philadelphia investigation touched off a national controversy last month when it was learned that Eilberg had called President Carter in November to urge the replacement of David W. Marston, the U.S. attorney there.

Marston has since left office. But it has become clear that an organized crime strike force headed by John Dowd in Washington - rather than Marston's office - provided the impetus for that inquiry by obtaining Elko's testimony in December.