Every Christmas since he was named FBI director three years ago, Judge William H. Webster has sent the same Christmas card to Judge Griffin B. Bell, the former attorney general who hired him.

"Three years ago, you ruined my Christmas," last year's card read. "Two years ago, you ruined my Christmas," said the card he sent the year before. And so on.

The way things are going at the bureau these days, Judge Webster will probably be sending Judge Bell the same Christmas card for at least the next seven years. Starting the fourth year of a 10-year term, Webster, only the third FBI director in history, has already left his stamp on the 46-the-year-old agency, which FBI-watchers say has accommodated itself to his quite style.

"Bill has his team in place at the bureau right now," said Judge Charles B. Renfrew, who was deputy attorney genereal during most of Webster's first three years at the FBI and knows him as well as anyone. "The bureau you see in operation today reflects his choices and his personality."

When Webster arrived three years ago, the bureau was in turmoil. Committees in both Senate and House had it under investigation; it had a reputation as almost an outlaw agency.

Former acting director L. Patrick Gray and two other senior Former officials, William Miller and Mark Felt, were about to be indicted for condoning illegal break-ins.

Morale among the 7,800 agents was as low as it had ever been. Almost daily, news stories would remind the FBI's personnel that they had lost the public's esteem.

If he did nothing else in the last three years, Webster managed to get the FBI off the front pages of the nation's newspapers. Among other things, he stepped up enforcement of guidelines as to what could be investigated legitimately, and how. Partly because of this, some of the FBI's most vocal critics have become supporters.

"I think Webster has moved the FBI away from politics and toward a focus on real criminal interests," said Jerry Berman, director of the American Civil Liberties Union. "It's a healthy focus. The bureau is now focusing on real criminal acts."

Webster's style and personality are very different from those of J. Edgar Hoover and Clarence M. Kelley, the two men who preceded him. Webster dislikes police jargon and shuns the limelight; he systematically visits the agency's field offices and talks to agents. A former prosecutor, trial judge and appellate judge, Webster has brought diplomacy the FBI the job, and in the process has brought the FBI closer to other law enforcement agencies than it has been at any time in its history.

"Webster has led the FBI into a set of relationships that have bound the bureau and the Justice Department together," said Philip B. Heymann, who headed the Criminal Division at Justice during the Carter administration.

Webster has also brought the FBI back into cooperation with the CIA, the Secret Service and the Customs Service, agencies with which the bureau often openly feuded in earlier days. He has mended bureau relations with the New York City police department. There were times when New York's finest and their counterparts at the Bureau barely spoke.

Just as importmant, "the Judge" has brought the bureau into direct social contact with the 1980s. When Webster became director three years ago last Monday, there were few blacks, Hispanics, Orientals and Indians among the FBI's field agents. There were fewer women agents. Three years ago, the FBI's image was what it had always been, an organization run by white men.

Of the 1,200 new agents the FBI has recruited in Webster's three years, 94 are blacks, 89 are Hispanics, 19 are Orientals and eight are Indians. The FBI had 91 women agents when Webster came to the bureau. Today, it has 350 women agents. The white male image is changing fast. Of the 16 new agents recruited last year by the San Francisco office alone, two were white males.

Webster has shifted other emphases as well. No longer does the bureau chase stolen cars, though it does investigate rings that steal cars. No longer does it respond to every bank robbery in America, though it still has 400 agents assigned to bank robberies.

Webster's priorities are organized crime, white-collar crime and foreign counterintelligence. While Kelley had set the same priorities, Webster has clearly thrown the bureau into high gear along these roads.

The bureau had of its best years in 1980. FBI arrests of organized crime figures led to 597 convictions, easily the best the bureau has ever done. More than 3,200 white-collar criminals, including con men, embezzlers, swindlers and corrupt public officials, were convicted last year, also the best the bureau has done.

"I think we've clearly regained out mometum," Webster said in interview. "I think we're moving forward on a wide range of fronts, you can see it in the bureau's morale and discipline."

Civil libertarians credit Webster for the evenhanded way the bureau appears to be conducting its investigations. Gone are the black-bag days of illegal entries and wiretaps, of undercover infiltrations of student and political movements, of electronic surveillance of public figures whose crime may have been public outspokenness. Not once in the last three years has the bureau been sued by a citizen claiming that his constitutional rights had been violated.

Webster admits the bureau was under seige when he took over as director.

"The top executives were consumed in responding to charges, and we were having a hard time convincing the agents we could go ahead without major risks of lawsuits and prosecutions," Webster said.

"It was a rough time. People were talking about ripping J. Edgar Hoover's name right off the building. I had a learning process when I got there, I had more than most people realize to do at the bureau."

Webster decided that his first priorities were to restore morale and momentum to the bureau, restore public confidence in it and reach out to minorities to win their confidence.

He made speeches to groups like the anti-defamation League and the NAACP who'd never heard an FBI director speak to them before. He set up a working arrangement with the Urban League to screen black and Hispanic applicants for agents' jobs in the bureau.

"We had really not been recruiting, we'd been screeners of white male applicants," Webster said. "The bureau didn't know much about getting blacks and Hispanics to apply for jobs, because they didn't know how to get the word out to those groups."

Not only has Webster hired more minority-group members than any other FBI director, he's promoted more within the bureau, which now has a black agent in charge in Indianapolis and Atlanta, a Hispanic in charge in San Juan, a Hispanic number two in San Antonio, and an Oriental assistant in Albuquerque. The black in Indianapolis, Wayne Davis, soon will take over as agent-in-charge of the Detroit office.

Webster set out to restore morale in the field by visiting the field. In the three years he's been director, Webster has made almost 100 visits to FBI field offices, and has visited all but 10 of the bureau's 59 offices.

Rare is the occasion when Webster will involve himself personally in an investigation, but he was deeply involved in the delicate Abscame undercover operation. He watched endless hours of videotapes of agents' meetings with congressmen. He signed off on each and every one of the money offers made to the congressmen.

Webster is quick to defend Abscam and the payments of $50,000 bribes to congressmen. "I approved the individual payments. It was new ground, and enormously controversial. What I said was, let's be absolutely sure of our ground . . . but let's go forward."

And there remain some other problems. While the bureau has moved socially into the 1980s, it still lags a little. Homosexuals are still fired by the FBI. The bureau still will not tolerate a man and a woman employe living together without being married.

Webster plainly enjoys what he is doing, but just as important, perhaps, has not let it consume him.

As he summed up the other day, "I've liked practicing law, I've liked being a trial judge, I liked being a prosecuting attorney, I liked being an appelate judge and I like what I'm doing now. I always think that I'm on loan, and I can always leave when it becomes important to leave."