The DC10 crash that killed 273 persons in Chicago May 25 has brought sharply into focus something that neither the airlines nor the Federal Aviation Administration wants to admit - there is a maintenance problem in U.S. aviation.

Despite the splendid safety record of commercial airliners, FAA files for the last five years show thousands of violations of maintenance standards. Nobody knows how many have slipped by undetected.

The problems affect all planes and all airlines. Some examples:

On July 23, 1977, the crew on a Trans World Airlines Boeing 747 jumbo jet en route from New York to Madrid was forced to shut down two of its four engines halfway across the Atlantic due to a loss in oil pressure.The plane landed safely. The oil pressure dropped because maintenance personnel had neglected to replace the oil filler caps. A Boeing 747 can carry as many as 400 people. TWA was fined the maximum $1,000.

On Sept. 29, 1975, a Delta Airlines DC9 carrying 84 passengers was preparing to land in Atlanta when a light told the crew that the nose wheel landing gear was unsafe. It was decided to make an emergency landing. The plane touched down in good shape, but as it rolled toward the taxiway the nose gear collapsed. Maintenance personnel, it was determined, had improperly installed a hydraulic hose and the hose had interfered with the landing gear. Some of the passengers suffered minor bruises.

According to available records, the plane had made four flights with the hydraulic hose in that condition. Unspecified disciplinary action was taken, according to federal records.

From November 1974 to February 1975, National Airlines operated a DC10 for 340 flights with a damaged landing gear. The gear had been damaged when the huge jet fell off a jack, rendering the plane "not airworthy," in FAA LANGUAGE. National was fined $5,000.

On Oct. 27, 1977, a TWA crew on a Boeing 707 cargo flight made an emergency landing in New York after observing "two distinct white light flashes on the right side of the aircraft." It turned out to be a fire in one of the engines. Reason: a maintenance crew had neglected to latch the engine cover after working on the engine. As the plane gathered speed on takeoff, one of the unlatched hooks broke off and punctured a fuel line, thus starting the emergency.

Airline maintenance, and the FAA's supervision of it, will be a central theme in the next few days as the National Transportation Safety Board conducts a public hearing in Chicago into the American Airlines crash there. Five of the first 10 scheduled witnesses are from the line's maintenance base in Tulsa.

Safety Board Chairman James B. King has already told Congress that "there is no doubt in our minds" that a key part that failed in the crashed DC10 "was hit," and thus cracked, during maintenance.

The real question about the DC10 crash, then, according to a number of safety experts, is whether it results in a major shakeup in both airline maintenance practices and FAA supervision.

A Washington Post study of FAA files shows that these problems occur regularly in commercial aviation:

Airlines sometimes allow uncertified mechanics to do work meant for certified mechanics. If this is discovered, it usually results in an FAA "warning" to the airline. In some cases, a $500 fine is levied.

Repairs are deferred on parts the FAA considers critical to the safety of flight.

Maintenance logs are found with improper entries. These logs are essential to safety, because airplane maintenance is predicated on the replacement of certain parts after a specified number of flying hours. If the log books are faulty, then the replacement schedule is faulty.

Most FAA enforcement actions are taken against airlines for seemingly minor things, such as improperly installing a hydraulic hose, putting in the wrong part, or omitting a required inspection.

Over the last five years, 10 airlines have been fined a total of $187,000 for violation of various federal regulations, according to FAA Chief Counsel Clark Onstad.

The maximum fine the FAA can levy for a single incident is $1,000. That maximum was established by Congress and is considered ridiculously low by FAA inspectors in the field. FAA Administrator Langhorne M. Bond wants a $25,000 minimum, but has been unable so far to get that recommendation through the rest of the bureaucracy and up to Capitol Hill.

The FAA recently found a way around the $1,000 limit, however, when it told Pacific Southwest Airlines (PSA) it would be fined $385,000 for a series of maintenance violations. Theoretically, each flight made with a maintenance violation incurs a $1,000 fine. PSA has said it would fight the FAA attempt to fine and said the FAA allegations were incorrect.

If these violations are occurring all the time, where is the policeman?

Unions who represent mechanics at the major airlines told The Washington Post that one of the major problems in the field is that FAA inspectors never get out on the line, but spend all their time in the office pushing paper.

On the other hand, there is a lot of paper to push. George House, who is in charge of the FAA's maintenance inspection team at American Airlines in Tulsa, said during an interview shortly after the Chicago accident that directives and maintenance change orders "come out in stacks. We have to depend on American Airlines maintenance. They have 6,000 mechanics. There is no way for the FAA to hire enough inspectors to watch every mechanic." House has six inspectors working for him.

The airlines themselves say that there is no payoff for them in taking maintenance shortcuts."Look, if we aren't perceived as safe, then we're out of business," one airline maintenance executive said.

While that is obvious, the DC10 investigation itself has spotlighted flaws in the system.

The Chicago crash has been traced to a fracture in a major support structure that held the engine to the left wing of American Airlines Flight 191. That fracture, investigators have found, was caused by impact, not by fatigue. The impact probably occurred when American Airlines mechanics were utilizing a new maintenance procedure that saved time.

The same maintenance procedure had been tried at Continental Airlines earlier, and had resulted in impact cracks on the major metal support. McDonnell Douglas, the manufacturer of the DC10, knew about the Continental problem, yet apparently never recommended in writing against the questionable maintenance procedure.

The Continental experience was not widely disseminated to other airlines, although it was mentioned in passing in an information circular from McDonnell Douglas to airlines flying DC10s.

FAA inspectors may have witnessed the maintenance procedure, and may even known that it resulted in cracks, but if they did they did nothing to stop it.

In short, nobody recognized or acted on the problem until after the crash. At least eight DC10's were found flying around with similar cracks before the DC10 was grounded for 37 days. All of them were operated by either Continental or American.

"We are still considering enforcement action against both American and Continental" for operating planes with cracks in the engine support structure, Onstad said.

Last April, before the DC10 crash, FAA Administrator Bond told a reporter of his plans for reorganizing the FAA's entire safety administration structure. He had already told the industry, in a tough speech at the Aviation Club here, that he intended to step up enforcement and fines. Internal FAA reorganization has been taking place over the past few months while the public's attention has been on the DC10 investigation.

Part of that reorganization is designed to deal with a morale problem that, officials at all levels of the FAA now concede, hit the maintenance inspection ranks about four years ago. A headquarters reorganization then relegated maintenance to second-echelon status as the FAA's maintenance director became an assistant to aircraft operations.

"That hurt in the field," a senior FAA official said. "The perception went through very quickly that there was nobody in Washington capable of fighting the battles."

Bond's reorganization puts maintenance on an equal footing.

Another problem, according to Onstad, is that "it is very hard to get our cases tried in court" by the Justice Department. Onstad said that, in addition to heavier fines, the FAA will seek authority to inititate its own litigation.

The final question, one that Congress will have to answer, is how much regulation aviation operations and maintenance should receive. Each new FAA inspector costs taxpayer dollars and adds to the intrusion of the federal government into the private sector.