When Indian Prime Minister Indira Gandhi and Pakistani President Mohammed Zia ul-Haq meet here next Monday for the first time on the Subcontinent, they will be talking in a vastly improved atmosphere of Indo-Pakistani relations.

Neither side is expecting a breakthrough in old and seemingly intractable differences that have existed since the partition of India in 1947, particularly since Zia's visit will be little more than a brief stopover on his way to Indonesia, Malaysia and Singapore.

But Indian and Pakistani officials, while publicly trying to keep expectations low, privately say that conditions for improving relations have never been so good.

"The atmospherics for this meeting are propitious. You might say that the stars are coming together in the right configuration," said one Pakistani official directly involved in the summit meeting.

On the surface, the meeting seems little more than a formality, with Zia scheduled to spend only 3 1/2 hours here for a private meeting with the prime minister, followed by lunch. Both sides have stressed that there is no fixed agenda for the talks.

But the timing of the visit, which had long been sought by Zia but gently discouraged by Gandhi, has given the meeting added importance.

It comes at a time when the Indian prime minister has mellowed her criticism of Pakistan's arms purchases from the United States, saying in one recent interview with a Pakistani newspaper that India does not fear aggression from Pakistan.

For his part, Zia said at a press conference during his recent visit to Peking that he has no objection to India buying 40 Mirage-2000 jet fighters from France because "Pakistan is not in competition with India in any respect" and does not object to any neighbor finding a solution to its own security problems.

The meeting also coincides with subtle changes in relationships among the dominant nations in Asia, changes that have indirectly diminished the need for both India and Pakistan to draw other powers into their disputes. In the past India has been allied with the Soviet Union and Pakistan with China.

Recent improvements in Sino-Indian relations and a resumption of talks between the Soviet Union and China could indirectly help promote better relations between India and Pakistan, officials of both countries said. One result would be a lessened reliance by China on Pakistan as part of its anti-Soviet strategy, which in turn has been seen here as an attempt to diminish India's influence in the region.

G.K. Reddy, the authoritative columnist for the daily newspaper The Hindu who often reflects current thinking in Gandhi's councils, observed that "the changing character of the great power triangle in Asia is making India and Pakistan increasingly conscious of the need for some degree of understanding between them to prevent the revival of the old tensions in the Subcontinent."

Also, diplomatic sources said, Zia's meeting with Gandhi just a month before his scheduled visit to Washington would place the Pakistani president in a more favorable light in the United States, regardless of the accomplishments of the visit here.

A well-connected Pakistani official today also pointed to the Oct. 7 talks here between Gandhi and Bangladesh's chief martial law administrator, Lt. Gen. Hussein Mohammed Ershad, as a hopeful sign that India is embarked on a course of improving relations with all of its neighbors. The meeting, which was climaxed with the signing of agreements on several long-grating border issues, was the first between leaders of India and Bangladesh in eight years.

"It was a fruitful exercise, and it lifted the relationship out of a rut into which it had fallen. I would hope the same thing would happen here" when Gandhi and Zia meet, the official said.

He said he did not expect Gandhi and Zia to engage in substantive talks about the disputed status of Kashmir, over which India and Pakistan have fought two wars. He said he expected the talks to give impetus to the establishment of a joint commission on normalization and also to the on-again, off-again attempts to reach agreement on a nonaggression pact.

"If there can be a lessening of tension in the Subcontinent, if we can take one step to live in peace and normalization of relations with 800 million people, it doesn't matter what the other byproducts are," he said.