WASHINGTON (AP) _ U.S. airlines are being warned in the wake of a fatal crash in Denver to make sure that inexperienced pilots are not paired on the same flight.

FAA Administrator Allan McArtor said Thursday that an inexperienced pilot should be matched with a more senior pilot, and that a captain should not allow a co-pilot with less than 100 hours in a particular plane to conduct a takeoff in treacherous weather.

FAA concern about pilot experience increased as a result of the crash of a Continental Airlines DC-9 last Nov. 15 in Denver in which both crewmen were new to flying that type of aircraft. The co-pilot had flown only one previous trip on a DC-9, but was flying the plane when it took off in a snowstorm and crashed. Twenty-eight of the 82 people aboard were killed.

Continental officials have defended their staffing policies, noting that the captain of the plane had more than 12,000 hours of overall flight experience and that both men were trained and certified to fly the DC-9.

But McArtor said Thursday that as an ''exercise of caution'' airlines should not pair an inexperienced co-pilot with a captain who also might have had a relatively short number of hours flying a certain type of plane.

McArtor said he hoped the airlines would follow the FAA's suggestion, but warned that if precautions are not taken the agency may issue mandatory regulations.

At major air carriers, pilots normally are paired on the basis of chance within a specific type of aircraft fleet. The assignments are largely dependent on a bidding system for trips, which in turn is based on seniority, according to industry experts.

If an airline has a fairly stable workforce, the senior pilot, who would be the captain, generally would have considerably more experience with a particular plane than his co-pilot. But aviation experts say when a workforce is expanding rapidly even the captain may be relatively new to an aircraft, with little more experience than his co-pilot.

In the case of the Continental flight that crashed at Denver, the captain had about 12,000 hours of flying experience, but only 198 hours on a DC-9. The co-pilot had been hired by Continental only last summer and had flown only 36 hours on a DC-9, much of that during training.

McArtor said there is no indication yet that pilot inexperience was to blame for the Continental accident, but the FAA is asking the air carriers to ''be prudent'' and ''stress the importance of not putting two pilots in the same cockpit if they both have relatively little experience in the type of airplane they are flying.''

On another subject, McArtor said the FAA also is tightening the requirements on how quickly airlines must perform deferred maintenance.

He said that partly because of competitive pressures the air carriers have been guilty of ''gamesmanship'' by postponing such repairs as long as possible to keep aircraft flying. He did not mention any specific airlines, but said the problem in various degrees is industry-wide.

The FAA's tighter rules require such repairs to be made promptly - in some cases at the first stop where repair facilities are available, and within three days in the case of less crucial items, officials said.

These repairs involve equipment that malfunctions but need not be replaced immediately because the aircraft has adequate backup equipment that does the same job.