WASHINGTON (AP) _ Senate Republican Leader Bob Dole said Tuesday the United States should resume ''significant military aid'' to Contra rebels in Nicaragua if the government there fails to hold and abide by free elections.

Dole, in comments to the Commission on Free and Fair Elections in Nicaragua, said he is not optimistic about balloting in Nicaragua, particularly in light of ''the sham of a new election law'' he said had been adopted by that nation's leaders.

The commission is a privately financed group made up of three Democrats and three Republicans and established by the World Freedom Foundation, headed by prominent conservative L. Brent Bozell III.

Former Sen. Gaylord Nelson, D-Wis., co-chairman of the commission, said the panel hopes to establish guidelines and encourage the holding of free elections.

''It will then be up to Daniel Ortega,'' Nicaragua's president, he said. ''If he is sincere about his commitment to holding elections in Nicaragua early next year, he can accept our work and use it as a guide in implementing the reforms he has promised since he took office in 1979.''

The other co-chairman, Curtin Winsor Jr., ambassador to Costa Rica in the Reagan administration, also said, ''The choice will ultimately be made by Nicaragua's Sandinista government. I hope to join with my colleagues in offering them a clear blueprint for democratic commitment. ... Theirs will be the right to use it, or to give their people less than they have offered them.''

Ortega has signed an accord with four other Central American nations in which he promised electoral and other legal reforms to ensure fair general elections, which are to be held in February. Last week, his government rejected an opposition demand to negotiate further reforms.

The Nicaraguan leader has been on a tour of European capitals to seek additional economic aid for his country's troubled economy.

State Department deputy spokesman Richard Boucher, in response to questions Tuesday, indicated the administration has been encouraging the Europeans to hold off on such aid.

''Our position on assistance to the Nicaraguans is well known. We believe that economic assistance should be closely linked to Sandinista compliance with their promises to hold free, fair and honest elections,'' Boucher said.

Dole told the commission he hopes for free elections ''but, candidly, I am not very optimistic.''

''The record so far - as manifest, for example, in the sham of a new election law recently promulgated by the comandantes - is hardly encouraging,'' the Kansas Republican said.

''What if next February comes and goes, and there is no free election, perhaps not even any election?'' Dole asked. ''What if the Sandinistas 'win' the election through fraud, or lose the elelction but refuse to yield power?

In that event, he said, ''I hope that we will articulate and implement a policy that will apply direct and effective pressure on the Sandinistas, including through the resumption of significant military aid to a revitalized democratic resistance.''

President Bush, in the face of congressional resistance to continuing the Reagan policy of military aid to the Contras, recently reached a bipartisan agreement providing for non-military assistance subject to review by congressional committees. The Bush administration has abandoned plans to seek immediate military aid.

John Silber, president of Boston University, told the commission, ''I do not see anything in the upcoming elections but an opportunity to delude ourselves. I believe we are in a corner, waiting for the paint to dry.''

However, Allen Weinstein, president of the Center for Democracy, said the Nicaraguan government recognizes it is under intense international pressure to achieve acceptable ground rules for the February balloting.

The center is a Washington-based policy institute that has been invited by both the Nicaraguan govermnent and its opposition to send observers to monitor preparations for the election.