The Federal Aviation Administration yesterday approved procedures for a detailed one-time inspection of the engine support pylons on all DC10s, but said that "other inspections and even design changes could be required" before the grounded jumbo jet is permitted to fly again.

In a press release issued without comment in Los Angeles, the Faa said study of the DC10's wing slats must be completed before final arrangements are made to return the plane to service. Most aviation sources, including highly placed Faa officials, said they expect a final decision early next week.

The engine support pylon and wing slats are the two key elements believed to have failed during the DC10 crash in Chicago May 25 that killed 273 persons.

The support pylon and the engine fell off the left wing as the plane was taking off. The mishap severed the two hydraulic systems that keep the left wing's slats extended, and they retracted. The slats extend from the front of the wing during takeoffs and landings to give a plane extra lift. With the slats retracted on the left wing but extended on the right wing, the plane rolled out of control and crashed.

The pylon inspection must be on each of the 138 U.S.-operated DC10s, and must be conducted in the presence of FAA inspectors, the release said. Furthermore, a series of technical tests in addition to visual inspections will be conducted on the pylons.

Each inspection is expected to take about 50 man-hours. The FAA approved the procedures in advance of announcing a final decision on the DC10 so that inspections could be performed early, officials said. Inspections are expected to begin today.

Once the DC10 is returned to service, reinspections of parts of the pylon area will be required on a high-requency schedule. Some inspections will be needed as often as every 100 flying hours, according to sources That is nine to 10 days of normal service.

The pylons have been extensively inspected already and 91 airplanes were found to have some discrepancy in the pylon are, the Faa said. Many of those problems were "petty," one official said, although severe damage was found on some planes.

Any previously undiscovered discrepancies must be reported to both McDonnell Douglas, the DC10's manufacturer, and the FAA. The new inspection procedure will be issued formally as an airworthiness directive today or tomorrow, the Faa said, and then will carry the force of law.

McDonnell Douglas' appeal of the FAA grounding order is scheduled for a hearing here Tuesday unless the order has been lifted by them. Wednesday, new congressional hearings on the Chicago crash and the FAA'S efforts are scheduled by the Senate Commerce aviation subcommittee.