Joe Krahling got the emergency call at home that Saturday morning in January: hijacking in progress at Dulles International Airport.

For the next few minutes, Krahling was glued to the phone, hastily assembling what he later called his "cast of thousands": hostage negotiators, the Quantico-based FBI hostage rescue team, a helicopter, someone to deal with the media, agents to secure evidence, others to board the plane, sharpshooters, and so on.

As the 30-year FBI veteran prepared to leave for Dulles, where a man armed with a cigarette lighter and a cassette deck was threatening to blow up a New York Air flight from Newark, Krahling's mind turned to how times had changed.

"You know, 15 years ago," he said to his sidekick Ray Connolly, "we would have got the call, and you and I would have gotten in our car, driven out to Dulles, gone out on the Tarmac, got on the plane, gone up to the guy . . . and said, 'Hey you! FBI. You're under arrest.' It would have been over before the press ever arrived."

Joseph A. Krahling, 50, who says he had the most fun in his career solving bank robberies in Los Angeles, was named head of the FBI's Alexandria field office two weeks ago. He has been acting head of the office since May 1986.

Top priority for his 84 agents, whose jurisdiction includes many federal government offices and defense contractors, is white-collar crime and government fraud, Krahling said in a recent interview. In the past year, his office has more than doubled its convictions (from 20 in 1986 to 46 in 1987) for bribery and fraud.

"Here, with all the billions being spent in our back yard on everything from paper clips to space capsules, you cannot tell me there isn't a significant amount of frand for us to target," Krahling said.

One of Krahling's upcoming projects will be to oversee the relocation of the FBI office from its current cramped site in Old Town Alexandria to Tysons Corner, a move set for early 1988.

Krahling is no stranger to fraud. After 10 years on the bank robbery beat in Los Angeles -- "as far as excitement goes, you couldn't have had better cases" -- Krahling was reassigned to Washington, where he supervised agents probing public housing fraud.

"Hell, I didn't know what an escrow was," said Krahling, who was born in the District and is known for his "aw shucks," self-deprecating humor. Krahling, black-haired, six-foot plus and husky, is also known for his sometimes natty attire, a reputation recorded for history when he faced TV cameras after the Dulles hijacking dressed in a sports coat and ascot.

FBI agents in ascots? "That wasn't real smart," he said, laughing.

In 1983, Krahling became a supervisor in the civil rights and special inquiries section in Washington.

The D.C. resident said his interest in the FBI began as a child when his grandfather, former FBI photographer Joseph W. Krahling, took him on visits to the bureau. "I remember him taking me around the FBI headquarters when I was about 8 or 9 years old," Krahling said.

The senior Krahling, who worked with the bureau from 1934 to 1966, headed the FBI's photographic facility in its infancy. "He was the FBI's photo lab in the '30s."

Krahling, who is divorced, is one of five children, whose father, Joseph A. Krahling, was a deputy fire chief in the District.

Earlier this year, Krahling directed the successful resolution of an Alexandria kidnaping case that climaxed at National Airport. His agents captured the abductor, rescued the woman, Marjorie Mitchell, and recouped a $30,000 ransom.

Back in his office, Krahling was congratulating himself, he said, when he got a call from FAA police at National Airport. Why hadn't he told them what was going on right under their noses?

All he could honestly say, he recalled sheepishly, was that he forgot.

One thing Krahling doesn't forget, he said, is that he has gained "two marketable skills" from his FBI career: "I can shoot a gun, and I can keep a secret."

And he always reminds reporters who call him for tips, he said with a smile, "that you're asking me to give up one of my marketable skills."