A lawyer for Mobil Oil Corp. president William P. Tavoulareas yesterday questioned closely a Washington Post reporter about how he reported two stories that the oil company executive and his son contend were libelous.

Patrick E. Tyler, 30, a reporter at The Post since early 1979, explained in detail for the six-member federal court jury what his sometimes cryptic notes from his interviews meant to him and how he viewed the information he gained from his sources.

Testifying on the second day of the trial of a $50 million libel suit against The Post, Tyler acknowledged under questioning by John J. Walsh, one of Tavoulareas' lawyers, that he asked a source for the stories whether he knew someone who could "rifle the safe" at the oil company executive's New York home, but said that he now regrets the remark.

But earlier testimony from Sandy Golden, a former Montgomery Journal reporter who led Tyler in late 1979 to Dr. Philip Piro, a Baltimore eye surgeon who was then the estranged son-in-law of the elder Tavoulareas, also showed that Tyler was given to flip remarks about Tavoulareas and Mobil's reaction to The Post's stories.

Golden, who wanted to work on the Tavoulareas story in order to enhance his chances of getting a job at The Post, said Tyler told him that Tavoulareas met with Post executive editor Benjamin C. Bradlee a few days after the articles ran on Nov. 30 and Dec. 1, 1979, and that The Post editor "blew him out of the water."

Golden, listed as a special correspondent on the first story even though he did not write any of it, quoted Tyler as saying Tavoulareas "didn't challenge anything" about the stories' accuracy and that the oil executive "went home with his tail between his legs."

The libel case centers on two stories written by Tyler detailing how Tavoulareas set up his son as a partner in a London-based shipping management firm that has done millions of dollars of business operating Mobil-owned ships.

Tyler recounted for the jury the conversations he had with Piro, Peter Tavoulareas and George Comnas, the former Exxon official who said, according to the articles, that he was asked by the elder Tavoulareas to head the shipping management firm, Atlas Maritime Co., and was then forced to resign after a dispute with the young Tavoulareas.

Tyler said Comnas, who is being sued by the Tavoulareases in a separate case, told him that the elder Tavoulareas asked him to include his son Peter as an equity partner in the shipping firm.

Tyler said that when he called the younger Tavoulareas in London to discuss the details of the arrangement between Atlas and Mobil, Peter Tavoulareas said, "Atlas is none of your damned business."

Tyler said he only had a chance to ask the shipping executive one question during a brief interview. "It was a 30-second outburst and Mr. Tavoulareas hung up," Tyler said.