The escalating U.S. military aid program for El Salvador includes three types of aircraft that the United States has never before supplied directly to the Central American nation.

The controversial arms deal has been described officially as a replacement of aircraft damaged or destroyed by Salvadoran insurgents. But it marks the first time the United States has sent troop transports, observer planes and A37 attack planes, the Pentagon confirmed yesterday.

The equipment is to be dispatched as soon as possible, administration witnesses testified on Capitol Hill earlier this week, to meet an emergency created by the insurgents' strike on the government's Ilopango air base two weeks ago.

The transfer has touched off a confrontation in the House, where some members have complained that it raises the U.S. commitment to El Salvador's civilian-military junta. Several House Democrats are drafting legislation to block further aid, but so far they have not attracted wide support.

The additional $55 million to be committed by the Reagan administration comes from a special fund controlled exclusively by the president. Its use cannot be blocked by Congress.

A Pentagon spokesman said yesterday that $25 million of the money will be used to replace equipment damaged or destroyed at Ilopango. That will include C123 troop transport planes; A37 fighters, small subsonic jets that can drop small bombs but are normally used for supporting ground troops; O2 spotter aircraft, and six UH1 transport helicopters.

In the past, the United States has supplied only helicopters to the Salvadoran government, which obtained U.S. fighters, transports and other aircraft through third countries.

The remainder of the $55 million will be used to improve Salvadoran military communications and provide ammunition and training, the Pentagon said.

Administration witnesses this week described the emergency assistance as necessary to help the government cope with new attacks by guerrilla forces in what the United States claims is an attempt to undercut the March elections for a constituent assembly. The administration has described U.S. aid as essential to prevent a probable victory by the insurgents.

On another military issue, the administration was assured yesterday that there will be little congressional opposition to its plan to sell F16 fighter planes to Venezuela. Several members of the Senate Foreign Relations Committee expressed doubt about the sale, which would be the first introduction of the sophisticated jet fighters into this hemisphere outside of the United States.

But none of them moved to sponsor a resolution of disapproval aimed at blocking the sale.

Justifying the sale before the committee, Undersecretary of State James L. Buckley cited a Soviet arms buildup in Cuba and Nicaragua. He said that last year "the Soviet Union flooded Cuba with over 63,000 tons of arms, the largest inflow in 20 years."

Sens. Christopher J. Dodd (D-Conn.) and Larry Pressler (R-S.D.) questioned Buckley about the wisdom of introducing one of this country's most sophisticated aircraft into Latin America. Buckley said the Soviets had introduced comparable technology first by sending Mig23 jet fighter-bombers to Cuba.

The new agreement calls for selling 18 F16A and six F16B aircraft to Venezuela. The total cost, including training, spare parts and support, would be about $615 million.