House Democratic leaders last night abruptly rescheduled today's expected vote on their $30.5 million package of humanitarian aid for the Nicaraguan contras after Republican leaders proposed a $36.2 million alternative that would not include lethal military assistance.

The Democratic leadership, citing the need to educate its membership on the differences between the two plans, said the House would vote next week.

"Our uneasiness is that members don't know enough about the two packages," said House Majority Whip Tony Coelho (D-Calif.). "We don't want any misunderstanding at the last moment . . . . The leadership met and we don't feel it is appropriate to shove it at the members."

Though Coelho, who along with other Democrats had earlier expressed confidence that their humanitarian aid package would pass, said there had been no apparent "erosion" in support, Republicans suggested that the vote was postponed only because of fears the Democrats would lose.

"They must have realized it would be too close to call," said a spokesman for House Minority Leader Robert H. Michel (R-Ill.).

At his news conference last night, President Reagan did not express a preference for any particular plan, but he said he favored delivering assistance to the contras through the Central Intelligence Agency, which the Democratic proposal would prohibit.

Asked whether it was worth supplying humanitarian assistance without military aid to the contras, Reagan said, "Anything that will keep the freedom fighters as a pressure on the Sandinistas is worth doing."

The Democratic aid package was drawn up following the House's Feb. 3 rejection of Reagan's request for $36.2 million in new aid to the Nicaraguan rebels that included $3.6 million in lethal assistance.

The Democratic alternative, which is limited to food, clothing, medical supplies and shelters, was promised to moderate lawmakers whose votes were critical to defeating the president's proposal.

Despite apparent similarities in the two plans, Rep. Dick Cheney (R-Wyo.), third-ranking member of the GOP leadership, dismissed the Democratic proposal as "a garbaged-up package designed to give people political cover."

The $30.5 million Democratic package would provide about $14.5 million in aid to the rebels fighting the Marxist Sandinista government of Nicaragua, and a like amount for medical care for children who are war victims. Another $1.4 million would go to Indian groups that have opposed the Sandinista regime but which have recently negotiated a truce with the government.

The Democratic plan, which would extend through June and through the end of the year if a cease-fire is achieved in Nicaragua, would also bar any further military shipments to the rebels and shift delivery of the humanitarian aid to the Department of Defense with congressional oversight.

If no cease-fire is in place in Nicaragua by June 1, the Democratic plan would also permit another vote on additional aid if the House Permanent Select Committee on Intelligence finds that the contras, but not the Sandinistas, have negotiated in good faith. However, that subsequent aid request would be offered by the Democratic majority leader, not the Reagan administration.

Though the $36.2 million GOP alternative matches the Democratic offer of $14 million for aid to Nicaraguan children, it differs in several key respects.

The remaining $22.25 million in aid to the contras would be for two months, instead of four, the plan would permit continued CIA deliveries of aid, would give the president an open-ended commitment to another guaranteed vote on resuming military aid through the end of his term and it would permit deliveries of "nonlethal" aid that could include items such as Jeeps and helicopter spare parts.

The GOP plan would not include any arms and would prohibit delivery of previously authorized lethal aid that is still in the supply pipeline.

Next week's vote will come just four weeks after the House, by an eight-vote margin, defeated Reagan's request to give the contras another $36.2 million, including $3.6 million in munitions. The Democrats' slim margin was achieved when Wright promised a group of House moderates that he would offer an alternative of purely humanitarian aid.

Staff writer Lou Cannon contributed to this report.