The Pentagon's project officer for a futuristic air-to-air missile has recommended delaying production of the weapon, asserting that it is plagued with design flaws despite four years of testing and that its manufacturer lacks the capability to build it.

The evaluation, contained in an internal Defense Department memo, marks the latest blow to the advanced medium-range air-to-air missile (AMRAAM) and comes as congressional conferees are fighting over rival bills, with the House voting to kill the system and the Senate wanting to spend $200 million to produce 15 of the missiles next year.

"I believe there are too many unknowns regarding the AMRAAM program to make a production decision at this time," wrote project officer Jerry R. Miller in a memo dated May 21.

Miller said Hughes Aircraft Co., AMRAAM's manufacturer, has failed to resolve a number of design problems and has not learned how to "effectively operate" the equipment or processes needed to construct the missile.

Hughes continually reengineers the missile to make it "producible" or able to meet Air Force performance specifications, but "very few, if any, changes appear to be made for the sole purpose of reducing costs," he wrote.

AMRAAM, a projected $10.8 billion program intended to provide the supermissile of the 1990s for Navy and Air Force pilots, has encountered problems almost since the Pentagon contracted with Hughes for full development in 1981. Since then, its estimated costs have more than doubled, with each missile now expected to cost more than $400,000.

Hughes has run into controversy itself, with the Navy and Air Force cutting off monthly payments for several other weapons after finding serious quality-control problems at the company's plant in Tucson.

Two maverick civilian analysts working for the Air Force warned in 1984 that AMRAAM was heading for "disaster" but Air Force leaders, who called the missile essential to its future combat capability, denied that the problems were serious.

Although Defense Secretary Caspar W. Weinberger decided in January to defer purchases of AMRAAM until cost growth is contained, the White House asked Congress for $540 million to buy the first batch of 90 missiles in fiscal 1986.

The House voted to kill the program, complaining that Hughes' schedule for AMRAAM had slipped by two years and estimating that each missile would triple original cost projections by the time it rolled off the production line.

The Senate approved $200 million for 15 missiles next year, $65 million for advanced procurement and $100 million for additional research and development.

Miller, who works for the Pentagon's Product Engineering Services Office, said a Navy and Air Force survey team went to Hughes in March to determine whether the company was ready to produce AMRAAM, according to his memo.

He said the team found a "significant number of design issues" to be resolved before it is "advisable" to begin production. He said that "only a portion" of the weapon's major subsystems have moved from the design to the manufacturing phase, and that Hughes is having difficulty building many of the components designed by its engineers.

"The [company's] attitude," he said, "is that major subsystems will be transitioned when they are ready. No one appears to be willing or able to say just when these events may be expected to take place."

A spokesman for Hughes could not be reached.