Rep. Sidney R. Yates (D-Ill.), chairman of the House appropriations subcommittee that overseas the budget of the Smithsonian Institution, quietly declined last month to be reappointed as a Smithsonian regent. He said he had difficulties "reconciling" the two positions.

The Illinois congressman, first appointed a Smithsonian regent in 1975, said yesterday that he found it "awkward" to serve as a director of the museum and research complex, while at the same time serving as chairman of the House Appropriations Interior Subcommittee. This unit plays a key role in determining how much the Smithsonian receives from the U.S. Treasury each year.

Much like directors of a corporation, the 17 congressmen, senators and private citizens and the Vice President and Chief Justice of the United States ultimately are responsible for day-to-day operations and policy decisions affecting the semipublic, semi-private Smithsonian.

Yates said his decision not to seek another two year appointment as a regent had nothing to do with a General Accounting Office audit of the Smithsonian's books currently under way or recent articles in The Washington Post and other publications raising questions about the Smithsonian's financial practices.

The GAO audit was ordered last summer by the Senate Appropriations Subcommittee on the Interior and Related Agencies after that committee discovered a $1 million contingency fund maintained by Smithsonian Secretary S. Dillon Ripley.

Since the audit began, Ripley has resigned as a director of the American Security and Trust Co., where the Smithsonian maintains bank accounts. The Post has pointed out other Smithsonian financial arrangements, including the purchase of almost 1,300 acres of farmland in Maryland for a land preservation and research facility called the Chesapeake Bay Center for Environmental Studies.

As part of those purchases, the Smithsonian has agreed to let former owners live free in their manor houses and farm center property without fee.

Yates said he was learning "things I didn't know" about the Smithsonian in various news accounts. But the congressmen said he thought regents generally were well informed about Smithsonian activities.

Contributing to his decision not to seek another term as a regent, Yates said, was his inability to attend all the regents meetings because they sometimes conflicted with sessions of the House. This, Yates said, sometimes made it difficult for him to obtain information made available at the regents meetings.

A spokesman for Speaker Thomas P. (Tip) O'Neill, who appoints the three congressmen who served by statute as Smithsonian regents, said yesterday that O'Neill has not yet decided who will be appointed in Yates' place. The spokesman said there was a possibility that another House regent also may ask not to be reappointed.