Sen. Ted Stevens (R-Alaska) called for a full-scale re-examination of the Smithsonian Institution's relationship to the federal government yesterday after hearing Smithsonian officials declare that they could sell off the National Air and Space Museum or the Museum of Natural History without Congressional approval.

Stevens said the Smithsonian's present unilateral freedom to acquire and dispose of property and buildings bought or maintained with U.S. money illustrates a need for greater control by Congress over the semipublic, semiprivate institution, which is requesting $106.5 million in federal funds for the 1978 fiscal year.

Stevens is the ranking minority member of the Senate Appropriations Subcommittee on the Interior and Related Agencies, which ordered the General Accounting Office to audit the Smithsonian's books last year after the subcommittee discovered a secret, $1 million contingency fund maintained by Smithsonian Secretary S. Dillon Ripley, Stevens said several times during budget hearings yesterday that the Smithsonian's financial practices are unsatisfactory.

"There has been no allegation of impropriety on the part of you or your colleagues," Stevens told Ripley. "But we (members of the subcommittee) seriously question the fiscal policies of the Smithsonian as far as federal funds are concerned."

Among other things, the GAO audit found that the Smithsonian has created two private corporations to convert millions of dollars of federal money into "private money" each year, which the Smithsonian then spends without regard to federal restrictions.

The GAO auditors also found that the Smithsonian has committed itself over the years to major projects, such as the Cooper-Hewitt Museum of Decorative Arts and Design in New York City and the Chesapeake Bay Center for Environmental Studies near Annapolis, without informing Congress or seeking its approval.

These two additions to the Smithsonian's activities now require hundreds of thousands of dollars a year in U.S. support.

Yet Peter G. Powers, the Smithsonian's general counsel, said yesterday that virtually all Smith sonian properties, including the museums on the Mall in Washington, legally belong to the Institution and not to the federal government - despite the fact that handreds of millions of dollars in federal money has been spent over the years to build, improve and maintain them.

Asked by Stevens whether it is the Smithsonian's position that it could sell off these properties without Congressional approval. Powers responded unequivocably: "Yes . . . although I can't believe we'd do it" without informing Congress first.

Stevens told Powers that, in his view, Congress could no longer tolerate the present situation, under which the Smithsonian has great independence from the federal government while receiving approximately 90 per cent of its budget from the federal treasury each year.

"These must become federal properties if we are to continue to fund them with federal taxpayers' dollars," said Stevens, who was the only member of the subcommittee at the hearing. "There seems to be a growing feeling in the Congress that we ought to be more involved in the acquisition and disposition of properties belonging to the Smithsonian."

After the hearing, Stevens said in an interview that he thinks the time has come for Congress to conduct a complete set of hearings to determine whether The Smithsonian's relationship to the federal government, little changed since the Institution was created by Congress in 1846, still is appropriate.

At present, The Smithsonian is governed by a board of regents composed of the vice president of the United States, the Chied Justice of the United States, six members of Congress and private citizens. The composition of the regents reflects The Smithsonian's semipublic, semiprivate status.

The Institution receives private money from various endowments, other donations and fund-raising activities such as its museum shops and The Smithsonian Magazine. In addition, it receives millions of dollars in research grants each year from federal agencies for scientific research. The Smithsonian considers the money to be provate. It also receives $100 million a year in direct federal appropriations.

In its early years, the Smithsonian received about 10 per cent of its money from the federal government and 10 per cent from private sources. In recent years, the ratio has been reversed.

Committee source have said Stevens and other members of the appropriations subcommittee have begun to feel that Congress should have greater control over how the Smithsonian spends its federal money. This feeling has grown stronger, according to these sources, since the discovery of Ripley's contingency fund and the recent GAO report, which found that the Smithsonian has used its private spending and civil service requirements.

For its part, the Smithsonian has contended that Congress has not paid as much attention to the Smithsonian as it should have and has not provided it with the kind of flexibility it needs to accomplish its cultural and research missions.

For example, Ripley and Powers argued yesterday that the private corporations are necessary to get around federal requirements on hiring and expenditures so the Smithsonian can hire scientists outside the civil service rolls and also fund multiyear research projects.

Stevens said the Smithsonian should have asked for legislative authority to spend its money in the most efficient way rather than set up the corporations without informing Congress about them.

"I don't think we have any disagreement with the goals of the Smithsonian but we are supposed to be the committee that watches over the taxpayers' money," Stevens said near the end of the hearing, which will be continued at a date not yet set. "The problem is that you have a tradition of comingling public and private money in a way that the subcommittee finds difficult to accept, Stevens said.