The underground nuclear explosion with which India shocked the world four years ago turns out to have been less an achievement than was originally believed. According to reports here, the successful test followed two failures, and the yield from the blast was considerably less than had been predicted. Because of the low yield, the Indian government canceled a scheduled international seminar on its nuclear achievement.

The government decided instead to conduct more fission tests. It never did, however, and with the change of government last year it appears that India has terminated its explosive nuclear ambitions, at least for as long as Moraji Desai is prime minister.

The revelations about the apparent inadequacies of the nuclear program appeared in the Madras newspaper, the Hindu, this week, prompted by a resurgence of criticism of Desai's pacifist policies by the Hawks in the nuclear community. Scientists who developed the device that exploded at Pokhran in western India on May 18, 1974, are beginning to call for renewed testing of atomic explosives. They feel that India did not gain much from the 1974 program.

These scientists, among them Raja Ramanna, who will leave the Atomic Energy Commisssion soon to take an advisory post in the Ministry of Defense, are disappointed by Desai's apparent abandonment of their cause.

They believe that by rejecting nuclear testing Desai has lost a bargaining tool that might have won concessions from the Western unclear powers, and they object to his injection of moral considerations into what they believe should be a dispassionate dialogue among nations.

Ramanna will join the Ministry of Defense later this year as scientific adviser, but will have no specific responsibilities for advising the armed forces on nuclear armaments or preparedness. This omission that has led some of his colleagues to infer that the Desai administration is weeding out the hawks.

The news that two attempts to explode a nuclear device had failed before the successful test surprised Western military attaches here, but the suggestion that the bomb's yield was less than it should have been did not.

"We were all primed for this big symposium the Indians wer due to have," one diplomat said, "but then it slowly withered away, and we wondered what had gone wrong . . . we imagined the explosion had not been quite as they expected."