Rep. Samuel S. Stratton (D-N.Y.), a longtime foe of plans to expand the Capitol, said yesterday that he would attempt to block the $55-million proposal to extend the building's west front when the issue reaches the House floor soon.

The extension plan, Stratton said in a letter circulated to other House members, is "unnecessary, wasteful, damaging and deserves to be defeated." He asked for support.

Up to now, the proposal has not encountered opposition as it moved through the legislative machinery of the House. It was approved unanimously without debate by the House Appropriations Committee earlier this week.

The measure could reach the House floor as early as next week. Stratton said he would make a motion to eliminate the funds for the west front project.

Although chances seem slight for Stratton winning the issue in the House, the proposal is expected to encounter stronger resistance in the Senate. Sen. Ernest F. Hollings (D-S.C.), who successfully opposed the west front extension in past years, has said that he would seek to block it again.

The extension plan, which calls for pushing the center part of the building outward by 22 feet, is opposed by the American Institute of Architects.