The Carter administration asked House leaders yesterday to delay action on Panama Canal implementing legislation.

The request amounted to an admission that the bill would be defeated if it were brought to the floor today as planned. Last week, the administration organized a big lobbying effort that included former president Gerald Ford, former secretary of state Henry A. Kissinger, Labor leader George Meany and actor John Wayne, hoping that would change enough votes.

However, House sources said yesterday the bill was still about 20 votes short of passage.

The administration, at the same time it asked for the delay, sought assurances from House leaders that the bill would be brought up before the July 4 congressional recess.

Vice President Mondale and congressional liaison officials Frank Moore and William Cable asked for the assurances at a meeting with House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), but sources said O'Neill was noncommittal and the delay was "indefinite."

Merchant Marine Committee Chairman John M. Murphy (D-N.Y.), whose committee brought out a bill mnore restrictive than the administration wanted, said that continued delays on the bill had caused "a fall-off in public support."

Murphy said, for example, the American Legion had supported his bill, but now "pressures from inside the American Legion" had caused Legion leaders to change their minds.

He said it would "take more than a P.R. job" to pass the legislation, because many members had compaigned as disapproving of the Panama Canal treaties passed by the Senate last year, and viewed approving the implementing legislation as approving the treaties.

Meanwhile, the Panama Canal subcommittee of the Merchant Marine Committee heard close-door testimony yesterday from Defense Department witnesses about Panama's involvement in efforts to overthrow the regime of Nicaragua's President Anastasio Somoza.

Rep. Robert E. Bauman (R-Md.), who supports crippling amendments to make Panama pay for the cost of transferring the canal, said the testimony went beyond reports in open hearings last week of Panamanian gun running to the Nicaraguan rebels. Bauman said he would ask for a closed-door session of the House to hear the testimony when the implementing legislation came to the floor.

Bauman and about 100 other House members were invited to the White House last night as part of the administration campaign to win votes for the legislation.

The legislation would provide for an orderly transfer of the canal to Panama in 20 years. In the meantime the canal would be run by a commission of U.S. officials and Panamanians. The legislation provides for moving military facilities, early retirement and transferring property.