Communist China yesterday became the fifth nation to explode a nuclear bomb.

President Johnson confirmed that the Chinese had detonated a "low-yield" atomic bomb, but cautioned that "its military significance should not be over-estimated."

Experts appeared to agree on two points:

* that it will take from four to ten years before the Chinese can develop an operational nuclear delivery system

* that the atomic test, coupled with the dismissal of Soviet Premier Khrushchev Thursday, has given a large boost to Chinese prestige.

Apparently the Chinese do not presently have the ability to produce large amounts of plutonium, the bomb's fissionable material. Some experts even speculated that yesterday's test device may have nearly exhausted their present supply.

China's first operational nuclear force will probably have a limited range. Morton H. Halperin, assistant professor of Government, estimated that within three or four years the Chinese "will probably develop bombs compact enough to put in the few bombers they have."

Intercontinental Capabilities

By the late 1960's or early 1970's, he believes that the Chinese will have perfected a medium range missle with a radius of about 1000 miles. Halperin, who is finishing a book, China and the Bomb, does not believe that the Red Chinese will possess significant intercontinental capabilities for another 10 to 15 years.

Yesterday's test caught few experts by surprise. On Sept. 29, Secretary of State Dean Rusk announced that the United States expected the Chinese to set off their first atomic bomb "in the near future."

Despite its limited military implications, the test--following Khrushchev's dismissal only by a day--could affect the current Sino-Soviet split. Richard E. Pipes, profesor of History, joined Halperin in speculation that the two events might lead to talks between the feuding communist nations.

Pipes said that the test served to strengthen the Chinese bargaining position. He noted that Khrushchev had planned a meeting of the world's communist parties for Dec. 15, which, in effect, would have "formalized the breech." Pipes said cancellation of this meeting would be a good indication that the new leadership might attempt a rapprochement.