Holiday Inns Inc. is discussing the possible sale of its bus subsidiary, Trailways Inc., with the Hillman Co., a privately held Pittsburg concern with interests in energy, real estate, barges and trucking, sources close to the bus company said today.

The Memphis-based hotel company confirmed reports Tuesday that it was holding discussions about the sale of Trailways but declined to disclose whom the talks were with or when the deal might be completed.

A spokesman for Holiday Inns refused to confirm that the company is talking to Hillman and would not say when the two firms might have an announcement.

"It would be completely premature to say anything," Holiday Inns spokesman Nicholas Biro said, "If we had anything, we would put out an announcement. We have just not progressed to a point where we have anything substantial to report."

A spokesman for the Hillman Co. in Pittsburgh also refused to comment on the negotiations. "We don't have any comment on it," said Mark Laskow, associate general counsel for Hillman. "That's just a plain-vanilla no comment. I don't know that there will ever be a time that we will have any comment on it."

While officials of Hillman declined to comment, sources close to the firm said the company is largely held by the Hillman family, regarded as one of the nation's wealthiest,and in Pittsburgh second only to the Richard King Mellon family. Today, the firm is headed by Henry L. Hillman, who took control from his father, John Hartwell Hillman Jr.

The Hillman firm, which has been described as a mini-conglomerate," has interests in coal, real estate and real estate development, barge construction, banking and trucking. The Hillmans do not talk with the press and have never stated publicly the value of their holdings, but an article in the Sept. 15, 1969 edition of Forbes placed Henry Hillman's value at $300 million, the company's revenues at $1 billion and assets of around $3 billion.

An affiliate of the Hillman Co. signed a definitive agreement June 19 to purchase M. S. Ginn & Co., a D.C. office supply business. If shareholders approve the sale, they will make $10.75 a share in cash or bond fund shares.

Sources close to Trailways said the bus company's president, J. Kevin Murphy, has been relieved of his duties, but will be allowed to maintain an office and secretary in the firm's Dallas headquarters until he finds another job. Holiday Inns declined to comment on the report, and Murphy could not be reached for comment.