The federal Aviation Administration said today it is conceivable that the grounded DC10 jumbo jets could return to service within a week but first at least one critical safety issue must be resolved.

This involves the slats, the control surfaces that extend from the leading edge of the DC10 wings during takeoff and landing. Slat problems are believed to have been a major factor in the DC10 crash in Chicago May 25 that killed 273 person.

The other major issue that developed as a result of the inquiry into the accident - the structural integrity of the support pylon that holds the DC10 engine to the wing - has been resolved "at the technical level," Jonathon Howe, FAA deputy chief counsel said during an administrative hearing by the National Transportation Safety Board here.

The engine and pylon fell off the left wing of American airlines flight 191 as it was taking off at Chicago's O'Hare International Airport.

Regular inspections of the pylon area - perhaps as frequently as every 100 flight hours - will be required before the 138 grounded U.S. operated DC10s can be returned to service, FAA officials said. That does not means, they emphasized, that all issues concerning the pylon design are resolved, only that the inspection program will guarantee that the plane is safe to fly.

That leaves the slats. "We are hopeful we can resolve that within a week," Howe said at the hearing. However, he said in an interview later, resolution of the technical issue would not necessarily means the jumbo jet could resume flying.

It must be decided if a design change is required in the DC10 slat system. If so, it must also be decided if that change must be completed before flights resume or if a high-frequency inspection program would guarantee the plane's safety until the change is made.

In the Chicago accident, the slats on the left wing retracted shortly after takeoff because they were deprived of the hydraulic fluid that keeps them extended when the engine fell off. The slats on the right wing remained extended. That created an unblanced control situation, and the plane rolled to the left and crashed.

NTSB administrative law judge William Fowler held a hearing in the Los Angeles Country courthouse today despite the fact that the full board had ordered a stay of the proceedings so it could decide two appeals pertaining to the case.

Fowler said he had not received a copy of the order and would start the hearing. The order arrived during the noon recess and Fowler postponed the hearing, complaining that "I would not have granted a continuance, but I bow to the power of the safety board." The hearing was generated by McDonnell Douglas, the DC10 manufacturer, when it appealed the FAA's June 6 order grounding the airplane.

Both the FAA and McDonnell Douglas sought delays today, arguing that the time of their technical people could be better spent working on the problems of the DC10 rather than in a courtroom.

The judge and attorneys for three airlines using the DC10 and the Airline Passengers Association insisted that the hearing continue. McDonnell Douglas attorney John Hennely complained that the FAA had not told McDonnell Douglas what was wrong with the DC10. "We have no evidence that could suggest in any way that the pylon or slat system does not meet the Federal Air Regulations," Hennelly said.

If the DC10 is returned to service before the hearing resumes, the entire NTSB hearing would become moot.

Frank Costello, an attorney for World Airways, charged that the FAA was on a fishing trip and would continue fishing until it found something wrong with the DC10. "Seven hundred eighty eight of our employes are out of work," Costello said. "The only way to bring this to a head is to go to trial."

Kenneth Teasdale, representing Trans International Airways, a charter carries, said that 1,504 persons had been stranded in Europe because TIA could not use its DC10. The number of stranded will top 6,000 by the end of the week, he said.

Howe responded that "everyone seems to be forgetting that there was a catastrophic accident occasioned by a serious structural failure of the aircraft." The airlines have argued their interest, and it seems to me it is clearly economic . . . the Federal Aviation Administration is charged with assuring the safety of the American public."