Leaders of the U.S.-backed Nicaraguan rebels met yesterday with Secretary of State George P. Shultz to deliver their latest description of principles for formation of a provisional Nicaraguan government.

Shultz, accepting the six-page document at his State Department office, issued a statement saying he was "delighted" to receive it. A scheduled news conference was canceled in the wake of the space shuttle tragedy.

"This document is of major significance to all of us who are concerned with progress toward democracy in Central America," Shultz's statement said. "It represents a program for democratic reform in Nicaragua and emphasizes the rule of law and healthy respect for human rights."

The paper, first made public Jan. 22 in Venezuela, promised national elections in Nicaragua two years after establishment of a provisional government, but did not say how or when that government is to come about. Its dissemination here is apparently part of the administration's effort to respond to members of Congress who have asked for firm democratic commitments from the contras, or counterrevolutionaries, as a condition for receiving military aid.

Adolfo Calero, one of three United Nicaraguan Opposition (UNO) leaders who met with Shultz, told reporters after the 40-minute encounter that he expects the Reagan administration to ask Congress soon for "$50 million upward" in aid for the rebels, including "about $30 million" in humanitarian aid.

"Things look a lot better than they did before to obtain the necessary support which we need," Calero said.

Administration officials have said the request could total as much as $100 million, but that it will not be submitted until they are sure Congress is willing to provide it. The existing $27 million humanitarian aid program expires March 31.

Arturo Cruz, another UNO leader, said the document presented yesterday was "a proposal to the Nicaraguan people for a -- not the -- provisional government," and contained "more explicit" detail of proposals UNO made last March 1 in Costa Rica and again June 12 in El Salvador.

The third UNO official, Alfonso Robelo, said military aid is needed immediately. "Now is the time, if we don't want this thing to drag on forever," he said.

The UNO proposal reiterates earlier promises to observe human rights, the rule of law, representative democracy and freedoms of speech, association, worship and unions.