A House subcommittee investigator testified yesterday that in 1979 he provided several documents about the business dealings of Mobil Oil Corp. president William P. Tavoulareas and his son Peter to a Washington Post reporter in the hope of gaining "some publicity" for congressional hearings into the transactions.

Peter Stockton, testifying under subpoena on the 11th day of the Tavoulareases' $50 million libel suit against The Post, said that Post reporter Patrick Tyler "seemed the most sensible person to release" the documents to since he was then working on a story of how the elder Tavoulareas helped create a London shipping management firm in which his son was a partner.

The information that Stockton released to Tyler formed the basis of Tyler's Dec. 1, 1979, story detailing a letter sent by Stockton's boss, Rep. John D. Dingell (D-Mich.), to the Securities and Exchange Commission. The letter, which has been described frequently in court, alleged that the Mobil chief may have given "false and misleading" statements to federal investigators in 1977 about the creation of the shipping firm, Atlas Maritime Co. The Tavoulareases allege that the Dec. 1 story and one the day before libeled them.

Stockton described conversations he had with Tyler and Sandy Golden, a special correspondent for Tyler's Nov. 30 story. It was Golden who led Tyler to one source for the story and then, while working on the story on his own, tipped Stockton off to the Tavoulareas business transactions.

Another House staff member, Michael F. Barrett, testified that the information he and Stockton collected, "some of which may have come from Mr. Golden," was then sent on to the SEC. The SEC in turn reopened its 1977 investigation of the Tavoulareas transactions. The investigation was later closed and no prosecution resulted.

Stockton acknowledged that he "quite often" leaked information to the press, saying that "whenever we're getting near the hearings, we like to release some information. Whenever you release some information to the press, you're always after some publicity."

But he acknowledged under questioning by John J. Walsh, one of the Tavoulareases' attorneys, that no hearings were scheduled when he leaked the documents to Tyler and none was held until last February, after Dingell was subpoenaed to testify in the libel case. The committee's hearings were not published until yesterday.

In other testimony yesterday, the younger Tavoulareas told the six-member federal court jury hearing the case that Atlas in the 1970s often had slim profits or lost money. But he acknowledged under cross-examination that a related company known as Anchor Insurance, in which he also had a 75 percent interest as with Atlas, often earned large profits, as much as $1.6 million in 1978.

The 32-year-old Tavoulareas said he could not recall many of the details about how the cash in the insurance company's bank accounts was spent on specified dates.

"I'm a lousy bookkeeper," Tavoulareas said at one point, adding that he left the financial details of his businesses to his accountants.

Another witness, Cass Peterson, a Post copy editor at the time who wrote a memo to another editor criticizing Tyler's Nov. 30 story before it was published, said she felt it "was not worth the length, which was 84 inches." Peterson said she felt that Mobil's participation in the Saudi Maritime Co. (Samarco), a shipping firm that then hired Atlas to manage its ships, was a more interesting aspect of the Nov. 30 story than the Tavoulareas business dealings on which Tyler focused.