The Senate inched toward bipartisan agreement late Thursday on a proposed aid package for Nicaragua's Contra rebels after Democrats promised to ensure a chance for a separate vote on military aid before Congress adjourns for the year. ``We're getting very, very close,'' said Sen. David Boren of Oklahoma, a pro-Contra Democrat, after a day of proposals and counterproposals between the two parties. A key to reaching agreement appeared to be a new letter from House Speaker Jim Wright, D-Texas, promising to bring any request from President Reagan for weapons aid for the rebels to a quick vote. The letter, Boren said, would include a guarantee that Congress would not adjourn without acting on such a request first. Wright made a similar promise as part of an agreement on humanitarian aid for the Contras last March, but several Republican senators said they needed stronger assurances. ``There's a great deal of suspicion of Jim Wright,'' said Sen. John McCain, R-Ariz. The negotiations, which included Reagan's national security adviser, Colin Powell, began shortly after the White House rejected a Democratic aid proposal that had been worked out a day earlier. Senate Republican Leader Bob Dole of Kansas drew up a list of objections to the Democratic aid proposal, and Democrats said later they were willing to make some minor changes in an effort to win broader support for the measure. ``We'd love to see Bob Dole and the Republicans join us on this,'' said Sen. Christopher Dodd, D-Conn. But Dodd added that Democrats would not budge on major aspects of the package because to do so would destroy the fragile agreement among Democrats that led to the proposal on Wednesday. The Democratic proposal, which defers action on lethal aid for the rebels until later this year, ``falls far short of getting any real hope for freedom and democracy in Nicaragua,'' said White House spokesman Marlin Fitzwater. ``Humanitarian aid is too limited, too narrowly defined, to be of any real help.'' But Fitzwater noted that existing humanitarian aid doesn't run out until Sept. 30, leaving time to work out a middle ground on the issue. ``There's a good chance for Contra aid legislation to pass,'' he told reporters. ``Legislators on both sides of aisle and the White House seem to share the feeling of outrage about the Sandinistas and support for the Contras, so I think there's a very good chance of passage of some kind of legislation.'' Fitzwater referred to recent actions by the leftist government in Managua to crack down on opponents, shut down opposition media outlets and expel U.S. diplomats. The most vigorous objection from Republican senators to the Democratic proposal was to its provisions setting up a later congressional vote on whether to resume the flow of weapons aid to the rebels. The package worked out by Senate Majority Leader Robert Byrd, D-W.Va., would require any presidential request for lethal aid to go for consideration first by the House, which has traditionally been more resistant to such aid. Republicans also argued that it would give undue influence to House Speaker Wright, an aid opponent. ``Nobody trusts the speaker,'' said Sen. Malcolm Wallop, R-Wyo., emerging from a meeting of Contra supporters. He said Wright has reneged on past promises as to when and how he would bring Contra aid to the House floor for a vote. Byrd characterized his aid package, worked out over two weeks of discussions with more than a dozen Senate Democrats, as one that would give incentives to both the Sandinistas and the rebels to revive and conclude their faltering peace talks. The proposal would provide an additional $27 million in food, clothing, shelter and medical supplies to continue current rates of such aid through next March. It also promises economic and trade assistance for Nicaragua if Managua goes along with ``a comprehensive final agreement to provide for peace and democracy in Nicaragua.'' Conversely, some $16.3 million worth of stockpiled weaponry could be released to the Contras if President Reagan certifies before Congress adjourns for the year that two of three conditions are met: the Sandinistas continue to violate terms of a regional peace accord; Nicaragua receives ``unacceptable'' levels of Soviet-bloc weaponry and the Sandinistas launch an ``unprovoked military attack'' on the Contras. But the weapons, withheld from delivery to rebel forces since the two sides entered a cease-fire earlier this year, would not be released unless both houses of Congress voted to accept Reagan's certification, with the House going first.