Senior Reagan administration officials yesterday, in a pessimistic assessment of the Philippine insurgency, said that the Communist rebels are growing stronger and more violent despite President Corazon Aquino's call for a cease-fire and reconciliation.

"The military situation is serious, and getting worse, with the Communists enjoying the initiative and assuming de facto control in areas where government influence has eroded over the years," Richard L. Armitage, deputy assistant secretary of defense for international security affairs, told the Senate Foreign Relations Committee.

Despite some military reforms by Aquino, the Philippine Army has been hampered partly because of a recent 14 percent cut in the military budget, he added.

The rebels "are not coming down from the hills" despite Aquino's amnesty offer, and recent ambushes by Communist rebels on government troops "leave little doubt in our mind that, at the end of the day, military action will be required to defeat the insurgency," Armitage said.

In comments after the hearing, Armitage said that only about 100 Communists have surrendered, according to U.S. estimates, a number offset by the increasing number of armed insurgents, now estimated at 22,500. This number is significantly higher than previous estimates of 16,500 armed guerrillas.

The grim assessment of the cease-fire program, on the eve of Aquino's 100-day anniversary as president, seemed to contrast sharply with more optimistic statements by government officials and supporters in Manila.

Philippine Ambassador Emmanuel Pelaez said after yesterday's hearing, "I think it is better than the way it's been assessed. They [the Communists] have lost their civilian base."

More than 800 persons have been killed in clashes between Communists and government troops since Aquino came to power Feb. 25 after a popularly backed military uprising against the 20-year rule of President Ferdinand Marcos.

Armitage and Assistant Secretary of State Gaston Sigur praised the new government's early reforms of the military, including the removal of 24 generals past retirement age and the dispersal of security forces from Manila to the provinces. These changes, they said, have enhanced the image of the armed forces and helped overcome a reputation for human rights abuses.

But the Philippine army "continues to be handicapped by inadequate resources," Armitage said, partly because of congressionally mandated reductions in U.S. military aid as well as Aquino's recent cuts in the 1986 defense budget.

"A pay raise announced in March has yet to be implemented . . . with further cuts anticipated in the months ahead," Armitage said. "Under such circumstances, we cannot expect an immediate and complete eradication of corruption and human rights abuses."

The administration officials made their remarks during a hearing primarily focused on the Philippine economic situation and the administration's proposal for $100 million in new economic aid and $50 million in security assistance to Manila for the current fiscal year.

At the hearing, Sen. Richard G. Lugar (R-Ind.), chairman of the Foreign Relations Committee, proposed an additional $100 million in economic aid for next year.

Armitage and Sigur spoke of an effective counterinsurgency strategy in the broader context of the Philippines' tight economy. Sigur said the economy, unlike the security situation, offered "great potential for a relatively quick turnaround." He pointed to a low inflation rate, reduced interest rates, a stable peso and increased international reserves as evidence of a "relatively good" financial outlook.

But some Philippine experts painted a bleaker picture. At a luncheon held yesterday by the Asia Society, Omar T. Cruz of the economic forecasting unit for the Philippines Center for Research and Communication predicted a zero growth rate for 1986 -- up from negative growth in previous years -- and said many firms are operating at only 50 percent capacity.

"Business has not shown any real indication of improvement," he said.