U. S. District Court Judge Frank M. Johnson Jr. declined his appointment as FBI direct yesterday in view of his unexpectedly slow recovery from major surgery.

Nominated by President Carter in August, Johnson, 59, said in a prepared statement issued in Montgomery. Ala., that he would need several more months "to regain my strength and stamina."

In light of that, he said, it would "not be fair to the Federal Bureau of Investigation or me to keep this matter pending any longer."

Attorney General Griffen B. Bell said he would "let the dust settle" for a couple of weeks before deciding on how to renew the search for an FBI director.

"Hopefully, during that time, names will occur to me," Bell said at a new conference. He said he would have preferred to wait for the judge to recuperate even if that entailed a delay until late spring or early summer. "Judge Johnson would have made an ideal leader for the FBI," Bell said.

Voicing the same sentiment, White House press secretary Jody Powell called the withdrawal "a loss to the administration, to the FBI and to the country - and we regret it very much."

FBI Director Clarence M. Kelley, the third man to head the troubled agency since J. Edgar Hoover's death in 1972, had been scheduled to retire Jan. 1. He has said he could stay through January but would have to leave then because of commitments to teach police science and begin legal practice and consulting work.

Bell met with Kelley for 30 minutes last evening, presumably in an effort to persuade him to stay until Feb. 15. An announcement is expert today.

Reputedly tough on criminals but best known for landmark rulings that desegrated Alabama schools and prisons and guaranteed mental patients' right to treatment, Johnson had been President Carter's first choice as FBI director, but turned the job down when it was first offered last December.

That triggered a seven-month search which resulted in several "finalists" but no choice. Johnson, a lifelong Republican and native Alabaminan, was nominated Aug. 17 after Bell heard that the judge was willing to reconsider.

Johnson then underwent a physical examination and discovered that immediate surgery was needed to correct an abdominal aneurysm, or swelling, of the main artery from the heart. He went back to work the day after his release from a Houston hospital and suffered a relapse a few weeks later. Doctors said he had developed a hernia in the goin while he was in Washington paying courtesy calls on a number of senators.

Attorney General Bell said less than two weeks ago that he still expected Johnson to recover in time for Senate confirmation hearings in January. In his statement yesterday, however, Johnson said that, while the operation appears to have been "very successful," his revory was "very slow." He plans to write the President a letter formally requesting withdrawal of his nomination.

Upon his selection, Johnson had said he hoped "I can be as fine a leader as J. Edgar Hoover." Bell said he still hoped to find someone with Johnson's characteristics.

Bell indicated he has someone in mind, but gave no hint of who that might be. He said the candidates recommended by a presidentially appointed search committee last summer still deserved consideration, but not exclusively.

The front-runners on that list were said to have been John Van de Kamp, district attorney of Los Angeles County, and Neil Welch, and FBI career man now in charge of the Philadelphia office. Another who was reportedly under serious consideration, although not on the list, was John A. Mintz, FBI assistant director in charge of the legal counsel division.