Federal aviation safety officials, citing three commuter airline crashes, are concerned about a sharp decline in the experience of the nation's pilots, especially those flying for the rapidly growing regional carriers.

"Commuter airlines are already scraping the bottom of the barrel in their attempt to provide pilots," National Transportation Safety Board Chairman James E. Burnett told a congressional subcommittee recently. "So we see levels of experience that are greatly reduced . . . and that is a disturbing situation."

The growth of regional and commuter airlines that has come with deregulation, coupled with the rapid expansion of many larger carriers, has opened the skies to thousands of new pilots. Many are being hired with fewer hours of flight time than most carriers would have accepted a few years ago.

Federal Aviation Administration officials, while worried that the rapid expansion of the major airlines will lead to a shortage of qualified pilots, say the system currently is safe. But they agree that the airlines require much less experience than in the past.

"Ten years ago, the typical person in the cockpit far surpassed our minimum regulatory requirements," said John S. Kern, director of the office of flight operations for the FAA. "Nowadays, we see that level coming closer to the minimum standards. The problem is clearest with the smaller carriers, and in the next year we will take a very strong look at our pilot training and experience standards."

Experience requirements vary from airline to airline and from plane to plane, but one key indicator of the declining level of experience is the number of hours a pilot or first officer has spent in the cockpit. In 1983, 8 percent of the pilots working for regional airlines had fewer than 2,000 flight hours. By last year, according to the Future Aviation Professionals of America, which monitors pilot standards, that figure had grown to 23 percent.

Although federal officials have yet to pinpoint the cause of the three commuter airline crashes, the experience of the crews is being studied as a possible factor. In one, the Sept. 23 crash of a Henson Airlines flight into a mountain near Virginia's Shenandoah Valley Airport, the pilot was flying a plane he had never flown until he was hired by the Maryland-based company a year earlier.

The plane's captain, former corporate pilot Martin (Ed) Burns, had logged more than 3,400 hours of flying, according to the NTSB, but he had never flown the 15-passenger Beech 99 until he joined Henson.

That accident, which killed all 14 persons aboard, and at least two others being reviewed by the NTSB have galvanized concern among federal officials over the decline in experience among the nation's commercial pilots.

The NTSB, which is charged with investigating all aircraft accidents, is evaluating the same issue in the March 13 crash of a Simmons Airlines flight in Alpena, Mich., that killed three people, and in last year's Bar Harbor Airlines accident near Auburn, Maine, that killed six persons, including Samantha Smith, the teen-ager who had become a celebrity when the Soviet Union invited her for a visit.

"In the past, the federal minimums did not apply because nobody in the industry would hire somebody on that level," said John O'Brien, director of engineering and air safety at the Air Line Pilots Association. "But that's changing. It's just hard to find that individual with 3,000 hours these days."

In 1983, the minimum amount of flight time required to be hired by small carriers was 1,200 hours. By last year, after the biggest growth spurt in the history of aviation, some airlines were hiring pilots with as few as 350 hours, only 100 more than the FAA requires for a commercial license.

Airlines also are relaxing requirements for age, vision, education and flight experience in an effort to keep full staffs. More than 8,000 pilots were hired by American air carriers in 1985, the largest number ever, according to the Air Line Pilots Association.

Dramatic airline growth in the era of deregulation is not the only reason for the surge. The generation of commercial pilots that came out of World War II and the Korean War is retiring. During the next 20 years, America's major airlines will lose at least 70 percent of their pilots to retirement, according to the pilots group.

As the smaller airlines watch the pilots they trained at great expense head for jobs with the bigger carriers, they are struggling mightily to absorb the losses.

The problems of Henson Airlines, the eighth largest regional carrier in the nation, are typical.

In 1982, Henson lost an average of less than one pilot each month. By 1983, the average was slightly more than one a month, and the following year the trickle had turned into a flood with an average of more than one pilot leaving each week. Last year, Henson lost 70 of its 220 pilots, and 19 have departed in the first three months of 1986.

"We are now looking for those people who are not quite as attractive to the big airlines," said John Presburg, Henson's vice president of development and scheduling. "With the seniority system we have, when you lose a captain you have to train everybody to move up a notch. It's a ripple effect that is felt by everyone. But before we would lower our standards we would curtail the growth of this company."

For years the military was the main source of pilots for the major airlines, with almost 75 percent coming from the Air Force and the Navy, according to statistics from the pilots association. The proportion of former military pilots has dropped to less than a third, partly because the military is training fewer pilots. That has forced the major carriers to turn to the regionals, and these airlines are often so small that training is a major problem.

"Training is the key to this entire problem," said John Lauber, a former human affairs specialist with the National Aeronautics and Space Administration who recently became a board member of the NTSB. "It is really the only way you can compensate for lack of experience. Today, we are hiring people who have not been forced to exercise their skills, and we need to enhance training within some of the commuters."

Lauber and the FAA's Kerns have said that it is time to decide whether pilot certification requirements should be changed for the smaller carriers. No thorough review of the issue has been conducted since 1978, when deregulation began.

The biggest training problem facing most regional air carriers is economic. For years, major airlines have used highly sophisticated flight simulators to help train pilots. These machines can cost millions of dollars -- as much as a plane in many cases -- and they are beyond the means of many small carriers.

"We have good people out there at the entry level, but it costs a fortune to get them trained," said Tulinda Deegan, vice president of the Regional Airline Association, which represents most of the smaller carriers. "You can't expect a small airline to spend $6 million on a simulator."

The FAA recently issued guidelines that would allow regionals more use of less sophisticated simulators for training, a move the commuter airlines sought. But the industry is not united on their use.

"Nobody around here wants to lower standards," said O'Brien of the Air Line Pilots Association. "But the key question is, how sophisticated does a simulator need to be to get good training?"

To keep the pilots they have, small carriers are turning to methods they had not considered before. Av Air (formerly Air Virginia) recently advertised for pilots and first officers, noting that it was interested only in local people.

"You have to figure out what your strengths really are," said Michael Campbell, an attorney who represents regional and commuter airlines. "You don't hire somebody from the West Coast to fly a local New England circuit. You remind people they will be home almost every night. And you raise pay."

Today, senior pilots at many regionals make more than they would if they switched to bigger carriers. Top pay at Ransome Airlines, for instance, is just under $50,000 a year for senior pilots. A pilot with 10 years' experience at Trans World Airlines makes virtually the same salary.

"It doesn't even matter, they want to fly jets," said Deegan of the Regional Airline Association. "In the end it doesn't matter how much we pay them or the routes they fly. A bunch of Ransome Airlines pilots just took a 50 percent pay cut to take off to People Express. No training is going to stop that."