The Bush administration, while praising a U.N. plan to hold elections to end the Cambodian civil war, urged Congress yesterday to continue nonlethal aid to two non-communist factions opposing the government installed in Phnom Penh by Vietnam.

Undersecretary of State Robert Kimmitt, testifying before a House Foreign Affairs subcommittee, declined to say how much aid the administration seeks. Earlier this year, it asked for as much as $7 million in overt aid and about $12 million in covert aid, according to informed sources.

The House, after a bitter floor fight, has approved the administration's request for overt aid. The Senate has not acted on that measure. The Senate intelligence committee rejected the administration's request for covert aid, but its counterpart in the House yesterday approved the covert aid, the Associated Press reported.

The U.N. plan would have international administrators run key government ministries and administer an election. It also calls for a cease-fire and disarmament of the rebel coalition and the government.

The approval last month of the plan by the five permanent members of the Security Council and general approval by Cambodian factions meeting in Jakarta, Indonesia, this week is likely to increase congressional support for aid to the non-communist resistance, sources said. The non-communists are in a coalition with the radical communist Khmer Rouge believed responsible for the deaths of more than 1 million Cambodians when it ruled the country from 1975 to 1978.

"As we make diplomatic progress, it is vital that we sustain our nonlethal assistance program for the non-communist resistance until an overall settlement is actually achieved," Kimmitt said. ". . . Cutting off aid to the non-communists would undercut their position and U.S. credibility and effectiveness just as the diplomatic process is accelerating toward a conclusion."

Asked by subcommittee Chairman Stephen J. Solarz (D-N.Y.) whether the two non-communist factions would continue their coalition with the Khmer Rouge, Kimmitt said he did not see why they would once elections approached. "I question whether they need to have any form of association with the Khmer Rouge at this time," he said.

Solarz, congratulating the administration and himself for the diplomatic success of a policy that he initiated, said opponents of the policy might want to cut off aid by arguing that an agreement was "virtually at hand" to end the fighting and have the United Nations take over the country and hold elections.

Kimmitt, however, referred to the recent diplomatic breakthroughs as "a significant point in the process, but it is still just a way-station toward a comprehensive political agreement that itself will be a way-station toward free and fair elections. We cannot delude ourselves into thinking that we're in the end game right now."

Critics of the U.N. plan have said it could require as many as 20,000 U.N. officials for a prolonged period to run the country and oversee disarming rival factions. There also is no indication how much the plan would cost or who would pay for it, although Kimmitt said yesterday that it was understood that the United States, the other permanent members of the Security Council and other nations in the region, such as Japan and Australia, would contribute to the effort.

Administration officials have estimated roughly that it would cost as much as $5 billion to implement the U.N. proposal. But sources said that figure was derived by doubling the cost of the U.N. effort to hold elections in Namibia, then doubling that again because a similar effort in Cambodia might take twice as long and then adding $1 billion because the Cambodia project would be more difficult.

Kimmitt, who acknowledged that the U.N. effort was a "rather ambitious undertaking" and that "sizable sums of money would be needed," said the $5 billion figure was "premature."