Congressional conferees have agreed to kill the Air Force's futuristic air-to-air missile unless Defense Secretary Caspar W. Weinberger can certify by March 1 that the weapon will work and cost no more than $440,000 each, congressional aides said yesterday.

Conferees who are ironing out House-Senate differences on the $302.5 billion defense authorization bill for fiscal 1986 also decided to direct the secretary of the Air Force to stage a competition among light fighter aircraft next year to help determine whether the F16 mainstay can be matched for cost and performance, aides said.

Both decisions reflect Congress' cost-cutting sentiment and impatience with the Defense Department's management of weapons procurement.

Aides said a conference panel was working on an agreement to resolve differences on modernization of the aging U.S. chemical weapons stockpile. They said the panel will recommend to the full conference language to resolve the key issue -- a House condition that European allies first vote to deploy the weapons.

The conferees' possible death warrant for the advanced medium-range air-to-air missile (AMRAAM) comes four years after the Air Force contracted for full development of what it called the supermissile of the 1990s for Navy and Air Force pilots, a weapon that could be fired from a jet fighter and destroy an enemy plane.

But the missile's projected costs have nearly tripled, and its Pentagon project officer reported in May that the missile still has design flaws and that the contractor, the Hughes Aircraft Co., lacks the capability to build it.

The decision by the conference committee represents a compromise between the House, which wanted to kill the program, and the Senate, which approved $241.5 million to produce 90 missiles next year, $101 million for further research and development and $66 million for advanced procurement.

The Reagan administration had asked Congress for $540 million in acquisition and research funds.

The compromise allows Weinberger seven months to certify that AMRAAM's design work has been completed, that it will perform up to original specifications and that total production costs for 17,000 missiles will not exceed $7.5 billion, aides said.

As a fallback measure, they said, conferees authorized $150 million next year to have several test missiles produced and to pay for the basic materials and equipment necessary to "qualify" a second contractor, Raytheon Co.

Another $101.4 million was authorized for research and development of AMRAAM in fiscal 1986, but $54.4 million is to be withheld until Weinberger certifies that the weapon meets performance and cost standards, aides said.

The decision to open a bidding war for light fighter aircraft for the first time in years marks a challenge to General Dynamics Corp.'s role as predominant producer of the plane. It provides an opportunity for Northrop Corp., which has offered to sell its F20 fighter plane at what it claims is a substantially lower price than the General Dynamics F16.

House members had voted for the competition to encourage a less expensive jet fighter. The Senate had taken no position on the issue.

Supporters of the F16 reportedly argued that cutting the General Dynamics order could result in higher unit costs for the aircraft.

Competition advocates, such as Sen. Pete Wilson (R-Calif.), countered that breaking General Dynamics' monopoly will serve as an incentive for price reductions.

General Dynamics, trying to head off Northrop, offered last month to sell a stripped-down version of its F16 for $10.9 million each, which is about $2 million less than the F20 and about $3.5 million less than the Air Force is now paying for the fully equipped F16.

Northrop developed its F20 Tigershark for overseas sales but has yet to sell any.

The Pentagon has acquired more than 1,300 F16s, whose costs have spiraled in recent years as General Dynamics has improved it with more sophisticated gear.