A National Airport custodian was killed when a pipe bomb exploded yesterday morning in an employees locker room less than 100 feet but four thick walls removed from the boarding area for the Eastern Airlines shuttle.

No one else was injured and only a few people in the airport even heard the explosion. Although security was intensified, there were no major delays in airport operations, spokesmen said.

The bomb was part of a booby-trapped Sears Craftsman tool box rigged to explode as it was opened, the FBI said. The custodian, identified by the Federal Aviation Administration as Julious B. Rogers, 51, was sitting on a chair, either holding the box in his lap or resting it on a table, when it exploded. He was alone in the room at the time.

Access to the employees' area is gained by pushing four digits on a combination lock. FAA spokesmen estimated that about 50 people would have reason to know the combination, which had been changed within the past two or three weeks.

Rogers staggered through an adjacent kitchen area and into a supply room before he died. He was pronounced dead on the scene by a doctor who had just arrived on the Eastern shuttle from New York.

An empoyee in a nearby Eastern Airlines office "felt" the explosion, in the words of an FAA official, and called the airport police. National Airport is owned and operated by the Federal Aviation Administration. A crime occurring on federal properly brought the FBI into the case immediately, although it almost always investigates airport bombings anyway.

Robert G. Kunkel, agent in charge of the FBI's Alexandria field office, said it was not known whether Rogers found the toolbox in the locker room, whether he picked it up elsewhere in the airport and carried it there, or even whose toolbox it was. The tool box had been in a shipping carton, fragments of which were found in the room where the explosion occurred, Kunkel said.

No motive had been found by the FBI, Kunkel said. Officials said they did not know whether they were investigating a murder or an attempted act of airport terrorism. No group or individual had called to take credit for causing the explosion, the FBI said. The bombing is apparently the

The explosive was apparently black gunpowder, placed inside a pipe eight inches long and three inches in iameter. FBI experts first thought the bomb was attached to a timing device, but rejected that notion after further investigation of the fragments.

There was little physical damage to the airport. Some powder burns were visible on the lockers and the table in the locker room was destroyed. Bloodstains trailing from the site of the explosion to the outer supply room were cleaned up before reporters were admitted.

Boarding areas for Eastern flights were the closet public areas. A snack bar and other facilities are located on the floor immediately above the room where bomb exploded, Saturday is normally the slowest day in the week at National Airport.

An individual could easily enter the corridor leading to the employees area where the bombing occurred, although signs on the doors to the corridor proclaim it a restricted area. However, a digital combination lock guards the door to the employees area. It was installed within the past two or three months as a part of an increased airport security program, an official said. Some employees said they asked for the lock after a petty theft problem cropped up in the locker area, but that could not be confirmed.

About 50 employees work out of the locker room and custodial offices. There are three shifts every day of the year, and each shift requires about 12 to 15 employees, FAA officials said.

Rogers, who operated heavy cleaning equipment, came to work at 8 a.m. yesterday. With fellow custodian Andrew Parker he had cleaned a floor in the nearby FAA police locker room. Before the bombing occurred, the two men split up while waiting for the floor to dry so they could polish it, the FBI said.

As a part of airport security procedures, all the airlines were immediately notified of a bombing and asked to search their immediate areas. Eastern changed planes for one shuttle. United Airlines and Braniff International ordered special searches of their baggage areas. Explosive-sniffing gdogs were brought in from an Army ordance unit at Ft. McNair. Nothing suspicious was found.

There have been few bomb threats at Washington area airports in recent weeks, according to James T. Murphy, director of Dullies International and Washington National.

"We know," Murphy said, "that any bombing sets off a flurry of bomb threats and also makes people nervous - if something doesn't look right, they're inclined to suspect a bomb."

In recent years, bomb threats at U.S. airports peaked at 383 in January, 1976, the month following the bombing at La Guardia Airport in New York. The La Guardia bomb," placed in a public locker area, killed 11 people and injured 70.

Security measures - including placing all public lockers behind security checking areas - were intensified everywhere, including the Washington airports. There have been 14 bombings at U.S. airports since 1971 and 2,605 reported bomb threats, according to an FAA report.

Rogers, the victim, was described by his supervisors as a reliable and efficient employee. He started with the FAA at National Airport in January, 1970, and was paid about $9,000 a year.

He was a widower and apparently lived alone, the FAA said. FAA officials were having difficulty locating Rogers' next of kin hours after the 11 a.m. bombing.

Rogers did "handyman jobs" on the outside snd "knew a lot about automobiles," according to James Brown, chief of the airport custodial branch.

Rogers lived in a one-bedroom apartment in Southeast Washington in a complex of two-story buildings. His landlady told a reporter that he had lived there less than a year.