The Reagan administration's Caribbean Basin plan suffered yet another reversal yesterday when a carefully crafted bipartisan agreement to push it swiftly through the House died on a point of parliamentary procedure.

The beleaguered plan, buffeted by critics in both houses of Congress for months, is the administration's major initiative in economic diplomacy this year and the subject of intensive lobbying recently.

But a compromise agreement that would have added the requested $350 million to a 1982 supplemental appropriation went down to defeat under a point of order because authorizing legislation had not yet passed the House.

The agreement would have included at least $75 million for El Salvador, the largest beneficiary, and was touted as necessary to rescue that nation from an economic morass as it resists leftist guerrillas in the countryside.

The point of order was raised by Rep. George Miller (D-Calif.) and others who said they objected in part to the way the money would have been divided among Caribbean and Central American countries.

A House rule, not always obeyed, requires that an appropriation be preceded by an authorization bill. The House Foreign Affairs Committee has endorsed a $350 million authorization but it has never been sent to the floor, partly because supporters think it would be killed by House hostility toward foreign aid in this election year.

A compromise worked out by the administration and Reps. Jack F. Kemp (R-N.Y.) and Clarence D. Long (D-Md.) would have given the White House a major victory. As its part of the deal, the administration had agreed not to push for a large separate package of military aid, including $35 million for El Salvador.

Kemp called yesterday's failure a "tragedy" for a major foreign policy initiative equal in importance to the post-World War II Marshall Plan that aided European countries.

The last chance for survival of the Caribbean plan would be Senate passage and House concurrence later this year, but that seemed doubtful. The Senate Foreign Relations Committee has transformed it, against administration wishes, into a World Bank plan. Republicans may try to reverse that on the Senate floor.

Other important parts of the Caribbean plan calling for investment incentives and trade preferences for several countries also have been blocked in the House. A Ways and Means subcommittee has loaded the trade section with protectionist amendments and the full committee has not even considered it.

The economic part of the plan that was defeated yesterday would have granted selected countries development funds and money to be used in generating local currency to help them overcome severe balance-of-payments problems.

At least one member of the group objecting on a point of order indicated that opposition to aiding El Salvador was part of their motive. Rep. Tom Harkin (D-Iowa) noted the large amounts of money allocated for that country and said many members favor cutting off aid because of El Salvador's violations of human rights.

Supporters pleaded for an exception to the House rule, saying that several of the beneficiary countries are confronted with communist insurrection and economic plight.

"We are facing a point of order when the world is in flames," said Rep. Joseph M. McDade (R-Pa.).

Meanwhile, administration officials encountered skepticism when they appeared before the House Foreign Affairs Committee to justify a report that human rights violations have declined and that land reform is progressing in El Salvador.

The report is necessary under a law requiring certification of those points in order to continue aid to that country.

"All available evidence suggests that the most serious violations of human rights--deaths attributed to political violence--are on a slow downward trend," Assistant Secretary of State Thomas O. Enders told the committee.

Rep. Michael D. Barnes (D-Md.) said the report "isn't convincing" because the accounts of civilian deaths are not based on first-hand information, Salvadorans being afraid to report killings by government security forces. Barnes said he is "skeptical" and will hold three days of hearings to get more facts.

Enders acknowledged that progress in prosecuting killers of four American church women in El Salvador has been slow because, amid the turmoil there, the judicial system is "non-functioning." He said that evidence gathered by a special commission was "conclusive" but that a successful prosecution requires a second investigation.