With a little less than three months left before the National Archives cuts its umbilical cord to the General Services Administration, speculation is growing over who will become the new U.S. Archivist.

After an initial flurry of names last fall, sources said the talk is now centered on former House member Barber B. Conable (R-N.Y.) and John C. Broderick, the Library of Congress' assistant librarian for research services.

Conable is an ardent history buff who owns a rolltop desk that belonged to Davy Crockett when he served in Congress from Tennessee. But Conable has said that he does not plan to remain in Washington.

Earlier, William J. Bennett, chairman of the National Endowment for the Humanities, and Mel Bradford, a Texas history professor who campaigned for Ronald Reagan in 1980, had been mentioned.

One senior Archives official said, "There's been no new talk of Bradford or Bennett -- both of whom seemed to be self-promoted."

Another federal official who watches personnel issues said that Bennett has been "looking for a bigger and better job everywhere in government. We don't really expect him to go to the Archives."

A White House source said yesterday that officials there haven't yet begun to focus on a nominee.

The Archives will become the National Archives and Records Administration on April 1. The current archivist, Robert W. Warner, will retire in mid-April, and Deputy Archivist George N. Scaboo is leaving April 3. If no archivist is in sight by mid-April, Claudine Weiher, now assistant archivist for program support, will take over temporarily.

Warner and Weiher have been working to restructure the agency in anticipation of independence.

Warner's office will add units responsible for internal auditing, congressional relations, legal services and public information, Weiher said.

Weiher will become assistant archivist for the office of administration, assuming new responsibilities for personnel.

James W. Moore, an assistant archivist responsible for the main collection, has been transferred to the new post of assistant archivist for the office of records administration. The unit will handle decisions on whether to retain government documents. Wilma Kriviski, who was director of the human resources office at the Civil Aeronautics Board, will direct the new personnel services division. NIXON TAPES MOVE TO SUBURBS . . .

For those interested in the expletives that weren't deleted, the Archives has shifted the listening booths for its tapes of Nixon White House conversations from its headquarters downtown to its annex at 845 S. Pickett St. in Alexandria. The 31 conversations that were used as evidence in the Watergate trials are available from 8:15 a.m. to 4:30 p.m. on weekdays.

The agency will let prospective listeners ride an employe shuttle bus that runs regularly between the offices. Listening booths can be reserved by calling 756-6498.

Other historic papers recently opened to public inspection at the Archives include:

* Documents and photographs filed in court for Sirhan B. Sirhan's trial for the assassination of Sen. Robert F. Kennedy.

* Microfiche of documents seized by the Army and Marine Corps during the U.S. invasion of Grenada in 1983.

* Correspondence between President Herbert Hoover and his wife, Lou, that had been ordered sealed until 20 years after the former president's death. A NEW LOOK? . . .

A Boston-based architectural firm has been hired to advise the new U.S. Archivist on redesigning and reorganizing the National Archives building.

"We have a building that was workable as a modern archives in the 1930s trying to pass as a building that would work in the 1980s," Weiher said. "It doesn't work."

Weiher said that the firm, Shepley, Bulfinch, Richardson and Abbott, will try to suggest ways to increase the building's exhibit space and provide a theater for films and lectures. SIGN OF THE TIMES . . .

An enterprising Archives official has made up a bunch of buttons that read: "National Archives Free at Last." They're on sale for 75 cents in Room 107 of the Archives Building.