The House Foreign Affairs Committee reached surprising bipartisan agreement yesterday on conditions for aid to El Salvador, although members disagreed on the impact of the language and the Reagan administration continues to oppose the provision.

The new language requires the president to "report," rather than "certify," to Congress that El Salvador has taken certain positions, achieved certain goals and made progress on others. Sponsoring Rep. Robert J. Lagomarsino (R-Calif.) called the agreement "a very significant development."

In another surprise, administration officials asked pro-Israel Democrats in a closed meeting to wait until mid-May before proposing that Israel be given a supplemental $1.44 billion in economic aid for fiscal 1985, according to officials who were present.

The administration has been pressing for structural changes in Israel's inflation-wracked economy before providing additional funds for this year. The request for a delay, made at a brief lunchtime meeting of the Foreign Affairs subcommittee on Europe and the Middle East, indicates little progress.

"We just don't want the committee to get too far out in front" of the administration, said Edward Fox, acting assistant secretary of state for legislative affairs, after the meeting.

Democrats are refusing to wait. Rep. Lawrence J. Smith (D-Fla.) said that the administration "had no new arguments" and that he expects the new aid request to be offered today, He noted that it will be "at least six weeks and more" before the request could become law.

Herbert Stein, a member and former chairman of the President's Council of Economic Advisers, described Israeli economic problems at the closed meeting, arguing that U.S. aid "cannot be a substitute for an effective [reform] program and should not precede its adoption." Smith and others have argued that Israel needs help immediately.

The full committee, wrestling with a total worldwide aid package of $13 billion, earlier approved an amendment banning direct and indirect U.S. aid to family-planning programs in China, citing concern that the communist government requires abortions as a way of ensuring one-child families.

The committee rejected a stiffer version, offered by Rep. Christopher H. Smith (R-N.J.), that would have ended funding for the United Nations Fund for Population Activities and for population groups that continue any type of work in China. The Senate Foreign Relations Committee passed a similar provision last week.

In considering provisions on Central America, Lagomarsino said requiring presidential "certification" of conditions for $922 million in aid could doom the bill and proposed that it instead require a presidential "report on the extent to which" the situation had improved.

Rep. Michael D. Barnes (D-Md.), chairman of the western hemisphere affairs subcommittee, proposed deleting "extent to which," so as to require that the president "report" improvements. Lagomarsino agreed, and the amendment was adopted.

The committee also approved a provision requiring the Salvadoran human rights commission to make a comprehensive report on probes into murders of Americans there.

It voted to make military aid to Guatemala conditional on installation of a democratic government and progress in human rights. It ignored an administration request for $25 million in fiscal 1986, allocating $10 million for medical and engineering aid.