The Soviet Union's economic and political pressure on the Sandinista government in Nicaragua was crucial to ensuring the free elections last February that ended the Sandinistas' 10-year rule, according to senior U.S. administration officials.

The Soviets, who also pressured the Sandinistas to back away from supporting rebels fighting the U.S.-backed government in El Salvador, withheld military and economic aid to Managua in response to persistent U.S. pressure and in an effort to remove Central America as an obstacle to improved U.S.-Soviet relations in arms control, Eastern Europe, trade and other issues.

The Bush administration publicly praised Moscow's cooperation after the elections last February. But the details of the Soviet actions and of the U.S.-Soviet diplomatic maneuvering, outlined in the current issue of Time magazine, show an unusual amount of coordination by the superpowers to resolve their differences in Central America.

The Bush administration, faced with congressional unwillingness to fund the contra rebels any longer, decided early on to try to force the Sandinistas to hold elections to legitimize their rule -- a vote the administration believed the Sandinistas could not win, according to administration officials.

That strategy could not work, however, without the backing of the Sandinistas' major supporter, the Soviet Union, which kept the leftist regime afloat by supplying about $1 billion a year in military and economic aid.

To enlist Soviet cooperation, Secretary of State James A. Baker III placed Nicaragua at the top of the American agenda of matters to be resolved every time U.S. and Soviet officials met throughout 1989. He convinced the Soviets of the importance of cooperation on Nicaragua both as a specific issue and as a broader test of Moscow's willingness to cooperate with the new administration to resolve regional conflicts in other areas, such as Afghanistan, a senior administration official said yesterday.

"We never believed that Central America was the key to improved superpower relations," Soviet Deputy Foreign Minister Viktor Komplektov told Time. Once it was clear Nicaragua was a major obstacle to improved relations, the Soviets strongly supported the election plan agreed to by the Sandinistas and the other Central American countries.

At one point, the Soviets turned down a Sandinista request for emergency funds shortly before the election, according to Time's account.

"They wanted money to put consumer goods in the stores, so they could portray the economic situation as improving and attract voter support," Yuri Pavlov, the Soviet Union's top policy assistant for Latin America, is quoted as saying. "We didn't think it was a good investment."

The Soviets also were key in ensuring that the Sandinistas agreed to a transfer of power to President Violeta Chamorro after the election, publicly pledging to respect the results and privately assuring the Bush administration that they would not supply weapons to the Sandinistas if Chamorro won, the administration official said.