The generation of military leaders who first saw combat in World War II began giving way yesterday to a younger group who fought the half-wars of Korea and Vietnam.

At a changed-of-command ceremony on the Pentagon parade ground, President Carter gave three new men certificates of office as the nation's top military officers.

The ceremony honored Air Force Gen. David C. Jones, chairman of the Joint Chiefs of Staff; Gen. Lew Allen Jr., Air Force chief of staff, and Admiral Thomas B. Hayward, chief of naval operations.

The three flag officers represent the majority of the Joint Chiefs of Staff, with the other member being Gen. Bernard W. Rogers, Army chief of staff.

In a phrase that symbolized the changes they represent for the nation's military establishment, the president praised Jones as "a statesman."

Jones' predecessor as chairman of the joint chiefs, Air Force Gen. George S. Brown, who will be 60 in August, was, by contrast, one of the colorful bomber pilots of World War II.

Brown was decorated for leading surviving B24 bombers back home from a famous low-level bombing raid against oil refineries at Ploesti, Romania, in 1943. He appeared to chafe in his armchair jobs at the Pentagon and elsewhere, several times getting himself in trouble by speaking his mind about alleged Jewish control of the media and the military burden of Israel.

Yesterday, at a ceremony saluting him at Andrews Air Force Base, the cancer-stricken Brown issue another warning about the Soviet threat, but chose his words carefully:

"I am concerned that the United States will not have the fundamental military strength necessary to meet our security requirements for the future. We surely will not unless we recognize now the impreative need to strengthen our defense."

Jones, when he briefly addressed the president and the Pentagon employes crowded onto the sun-drenched parade ground yesterday, promised as chairman "to speak out responsibly and forcefully" on military issues facing the nation. He pledged at the same time to carry out faithfully whatever decisions are made.

Jones, native of Minot, N.D., served at the end of World War II as an instructor pilot, but didn't experience combat until the Korean War. Carter, in hailing his new military adviser, told the crowd that Jones not only had flown 300 hours in combat missions over North Korea but is "a superb strategist."

Jones has gained a reputation within the civilian hierarchy of the Air Force as a skillful manager. His management jobs included commaneer of the Air Force chief of staff before succeeding Brown as chairman of the Joint Chiefs.

Among some fellow Air Force officers Jones is criticized for not putting up a bigger fight for the B1 bomber, which President Carter canceled in favor of the cruise missile.

As chairman of the joint chiefs, and this the military's channel to the president, Jones will play a key role in Carter's effort to win acceptance of a new strategic arms control agreement.

Like Jones, the new chief of staff of the Air Force, Gen. Allen, represents the new breed coming into the top command spots of the U.S. military. He did not graduate from West Point until 1946, after World War II, and looks the scientist that he is.

The president, during the ceremony of presenting white scrolls, called certificates of office, to the flag officers, hailed Allen's "superb qualities as a scientist." Allen, 53, has a doctorate in physics as well as 4,000 hours as a command pilot.

The third flag officer honored by Carter yesterday, Adm. Hayward, 54, also missed World War II. He was not commissioned as an ensign until 1947.

"I would have really preferred a submariner," Carter, the ex-submariner, quipped from the ceremonial platform yesterday. But, the president continued, Hayward, a Navy pilot who first flew as a pilot in Korea, is such "superb operational commander" that even submariners wanted him as the nation's top-ranking sailor.

"I'm proud to be with these leaders," Carter said of the new generation of flag officers.

The Army's representative, Gen. Rogers, 56, did serve during World War II.

(Marine Commandant Louis H. Wilson, also a World War II veteran, is not a regular member of the Joint Chiefs of Staff, but attends its meetings when Marine matters are under discussion.)

Carter, after pledging these new military leaders, vowed that for his own part he would "never permit our nation to be weak militarily."