Chief Judge Barnard F. Jennings, who is credited with transforming the Fairfax County Circuit Court into one of the speediest trial courts in the nation, is retiring after 23 years on the bench.

"I just really feel like I've been doing it long enough," Jennings said yesterday. "It's time for someone else to have a chance to come in with new thoughts and new ideas."

As chief judge of the circuit court for 12 years, Jennings has wielded tremendous power, including responsibility for assigning cases to the 10 circuit judges and overseeing administrative aspects of the largest and busiest circuit court in Virginia.

The new chief judge will be chosen by the other judges; the three leading candidates sources mentioned yesterday are William G. Plummer, F. Bruce Bach and Lewis H. Griffith. As for the vacancy on the bench, Jennings said it is unlikely that the governor would need to select an interim judge because the General Assembly, which will name his replacement, meets soon after his resignation takes effect on Dec. 31.

During an interview in his office yesterday, Jennings, 62, said the accomplishment he is proudest of is getting a new Judicial Center for the county.

Fairfax voters had rejected a bond referendum for the Judicial Center in 1972, but Jennings made it his priority after he was selected chief judge in 1975. With his lobbying, a second referendum was approved in 1976 and the Judicial Center, which houses the Circuit Court and the General District Court, opened in 1982.

County Board Chairman John F. Herrity, who helped Jennings lobby for the bond referendum, testified to Jennings' power yesterday upon learning of his retirement. "He could have simply ordered {the county board} to build a new courthouse. And it would have been done in about 10 minutes," Herrity said.

Jennings, who is paid $77,000 a year, also has received almost universal praise from members of the legal community for streamlining the circuit court.

His tactics, with the help of a court administrator, include moving toward automation, establishing early trial dates, using a "call-in system" for jurors to avoid long waits, adding extra grand juries so one sits every month and putting strict limits on continuances.

With a few exceptions, criminal cases are disposed of within 45 to 60 days and can even be heard within five to 10 days of indictment, Jennings said. Civil cases can be placed on the docket within six months.

Courts around the country are beginning to adopt practices that the Fairfax court initiated about six years ago, said Clerk of the Court Warren E. Barry.

"We've got one of the best-run courthouses," Barry said. "The judge and I have had our disagreements, but I have an ever-growing appreciation for his skills."

The quality for which Jennings receives adulation is also the one that has drawn fierce criticism: speed. Although his goals are praised, his methods sometimes are criticized. Many in the legal community have said that Jennings has been so intent on racing through the docket that he has cheated some people out of their day in court.

Some have expressed frustration with what one lawyer called Jennings' "unwillingness to listen to testimony." With the goal being economy of time, "he simply says to the lawyers, 'tell me what your witness would say,' " the lawyer said.

In one Virginia Supreme Court decision, the justices found no grounds for reversible error in a case Jennings presided over, but they did note his zest for speed. Said the opinion: "We are constrained to say, that it would be better procedure in a nonjury trial of a criminal case for the trial judge to determine the voluntariness of the confession before admitting it into evidence."

Despite the criticism, Jennings has earned praise as an administrator, including his creation of a conflict of interest list. To avoid even the appearance of conflict, Jennings directed the judges to maintain an updated list of lawyers who cannot appear before them because of business or personal ties. The list currently contains almost 200 names.

"There are few judges I've met in 18 years of law enforcement that I respect more," said M. Wayne Huggins, who as the county's sheriff meets with Jennings often about matters pertaining to the jail and courthouse security.

That respect extends even to security issues, over which Huggins has fought a losing battle. Huggins wants metal detectors installed at the entrances to the courthouse; Jennings does not.

Huggins said there is no question as to who runs the show at the Judicial Center. However, he added, there is a misperception among some around the courthouse that he is a man to be feared: "A call to Judge Jennings' office was tantamount to a visit to the woodshed with your father," Huggins said.

Although there have been persistent rumors of his retirement for years, word that he would be leaving effective Dec. 31 caught many in the Fairfax legal community by surprise yesterday.

"I'll be darned!" said former Fairfax Commonwealth's Attorney Ralph G. Louk, who attended George Washington Law School with Jennings and also worked with him as a fellow assistant commonwealth's attorney in the early 1950s. "I didn't know he was going to resign; he's so young."