Pathologists at the National Naval Medical Center in Bethesda began the task yesterday of identifying the burned and mangled bodies of 21 people killed in the fiery crash of an Air Force jetliner in rural Maryland.

The remains of all 21 victims had been recovered by late yesterday afternoon, an Air Force spokesman said. "We can't say corpse 'A' is individual 'B' but we have enough to say we have the remains of 21 people," an Air Force spokesman said. Among those killed were the wives of two crewmen and a civilian technician.

Searchers focused yesterday on recovering the bodies of all of the crew and passengers before turning to the wreckage, which they plan to piece back together at Andrews Air Force Base.

The jet, a four-engine Boeing EC135-N carrying sophisticated missile-tracking equipment, crashed Wednesday morning. No cause has been established and the FBI said yesterday that no evidence of sabotage has turned up so far.

At the Naval Medical Center, a team of 15 pathologists from the hospital and from the Armed Forces Institute of Pathology at Walter Reed Army Medical Center were working in refrigerated vans. The examiners in the institute's department of forensic science routinely undertake a process of identification in which various stations are set up where tissue samples are taken, teeth are x-rayed and personal effects are dried out and photographed.

After all the victims have been identified, the pathologists will study whatever human factors may have played a part in the crash, and examine the pattern of injuries. The findings will be reported to the Air Force Accident Investigation Board, the military panel looking into the crash.

At the crash site northeast of Walkersville in Frederick County, more than 80 military searchers trooped at arms' length yesterday through the knee-high stalks of wheat and rye, extending their search for body pieces and airplane wreckage in a radius of six to eight miles around the crash site. Here and there they spotted dog tags belonging to some crew members. So far all the bodies recovered have been in the main area of the crash.

Investigators, led by Brig. Gen. William T. Twinting of Vandenberg Air Force Base, located a 20-foot-diameter that they believe contains a large section of the plane, possibly the bulbous rada-dome nose. The crater smoldered through the night.

The cause of the crash is still unknown. "I have not confirmed there was an explosion or that it [the plane] came apart in mid-air," said Brig. Gen. Peter Odgers, who was in command of the search and rescue operation. Witnesses to the crash said they had seen or heard two or three explosions before pieces of the plane hit the ground.

The FBI assigned more than a dozen Baltimore field office agents to the crash site to act in a liaison capacity, although it is up to the Air Force investigators to determine the cause of the crash. The FBI also sent fingerprint experts to the medical center in Bethesda to assist in the identification of the bodies.

"We don't wait for an invitation. Whenever we have a disaster it's automatic that we appear," said Special Agent Edward Hegarty.

At Wright-Patterson AF Base in Dayton, Ohio, Force officers, sometimes accompanied by clergy, finished notifying the families of the 21 victims. Switchboards at the base were besieged by anxious relatives.

The two women killed, Peggy A. Emilio, 24, and Linda M. Fonke, 30, were aboard the jet with their husbands under the Air Force's "Have Partner" program, which allows spouses to fly to help them better understand their spouses' jobs.

The civilian riding along was Michael W. Riley, 24, a technician with Bell & Howell Co. who was monitoring a telemetry recorder, which records computerized missile data. "It's common practice for technical representatives to ride along," said Wright-Patterson spokesman Albert Swihart.

The jet had left the Dayton air base at 10 a.m. Wednesday on a training mission over the Atlantic Ocean when it crashed, 51 minutes into the flight.

In the aftermath of the disaster, security in the grain field near the Maryland Midland railroad tracks was tight yesterday as military personnel photographed the scene, marked bodies and pieces of wreckage and began to compile a map of the crash site. Searchers were also looking for a "loads recorder," a device aboard the plane that measures structural stress.

An FAA spokesman said yesterday that the Air Traffic Control recordings and computer readouts have been turned over to the investigating team.

The search attracted scores of local adventurers and curio seekers from the very young to the very old, who went up the railroad line and came back with smiles on their faces and pieces of the jet.

One man, a Hagerstown roofer identifying himself only as Sibert, walked two miles with a reporter along the tracks bordering the site, hopped a barbed wire fence, and happened on a flight bag containing a smashed banana. Nearby several soldiers discovered an arm with a watch on its wrist, still ticking.

James Stupe, whose farm received most of the debris, asked state troopers yesterday if he could "do a little farming soon" in the area where the tail section landed. Stupe, who was not allowed to walk on his property by Air Force officials, was told by the trooper to wait until the search was over.