The first $29 million to begin work on the long-stalled redevelopment of Pennsylvania Avenue, the nation's ceremonial main street, was approved yesterday by the House Interior Appropriations Subcommittee.

Part of the money, if approved by both the House and Senate, would rescue the historic Willard Hotel from the wrecker and clear the way for its possible renovation and reopening.

The U.S. Court of Claims ruled recently that the government, by refusing to permit the Willard's demolition by its owners, has in effect taken ownership to the structure and the government must pay them for it.The owners seek $8 million plus damages, but no final price has been set.

Yesterday's subcommittee action was coupled with a warning from Rep. Sideny R. Yates (D-Ill.), the chairman, that the whole Pennsylvania Avenue outlay "mya run into a lot of trouble on the (House) floor." Since the House dealt the project two severe setbacks last year, yesterday's action set the stage for a possible make-or-break decision.

Rep. Clarence D. Long (D-Md.) already has attacked the funding for the project, seeking to liken it to the National Visitor Center at Union Station, widely regarded as a costly fiasco. "I couldn't care 10 cents about the Willard Hotel," he said at a recent hearing.

Yesterday's decision was reached by the unspoken consent of the members present, without a formal vote. Long, attending another subcommittee meeting, was not there.

At a hearing Tuesday, Elwood R. Quesada, chairman of the government sponsored Pennsylvania Avenue Development Corp., insisted that the Visitor Center analogy is inaccurate.