New Delhi — Indo-American relations have lately tended to move at two levels. On the more visible plane they are evidently fragile, now improving, now stagnating, harmonious, or acrimonious depending on the issue of the moment. On the other plane, much less in the limelight, they have acquired a certain durability, even though progress tends to be measured in inches rather than yards, and there is a long way to go.
Secretary of State George Shultz's two days in New Delhi last week were, from this perspective, true to form.
Mr. Shultz, on his first official visit to this country, came across as a good talker and eager listener. By unofficial calculation he spent his first working day in almost eight hours of serious conversation, which by any standards was a great deal. But then, as an American official said, there were a lot of people to talk to, starting with Prime Minister Indira Gandhi and Foreign Minister P. V. Narasimha Rao and then other ministers, editors, economists, and businessmen.
On the volatile, visible plane, the curtain went up on the Shultz visit with a controversy in the Indian press featuring certain remarks of Ambassador Harry Barnes. Some Indians interpreted an interview that Barnes had given a week earlier to suggest that the Americans were advocating self-determination for the Indian state of Punjab which has seen a frequently violent two-year-old movement for greater autonomy within India's federal system. The movement has, however, an extremist fringe of expatriate Sikhs based largely in North America and England which advocates an independent ''Khalistan'' for its religious sect. There was tension earlier this year when the United States gave one of the leading advocates of Khalistan a visa to visit the US.
The Americans shot down the Khalistan balloon by reissuing a Shultz statement of last March which had sought to allay Indian anxieties when the visa was issued, and the secretary of state reiterated the American position - that the US government is interested in the integrity of India and not its breakup - in the various talks he had.
But if that was largely a question of deft diplomacy, Shultz was able to eliminate a more serious, potential source of trouble at the very start of his visit. Twenty years ago the US began to supply nuclear fuel for India's Tarapur reactor, built by a US company, under a 30-year supply contract. But when the US Congress passed legislation in 1978 banning the supply of nuclear materials to countries which did not submit their facilities - and India does not - to certain international safeguards, that flow was interrupted, suddenly raising a crisis in Indo-American ties. The fuel issue was solved last year when Mrs. Gandhi visited Washington, and France agreed to replace the US - with Washington's approval - as the source of nuclear fuel.
Shultz was able to write the second chapter in the Tarapur saga: the supply of spare parts for the two-decade-old nuclear facility. Tarapur has had safety problems, and it was this which enabled the US administration to sidestep a potential confrontation with its home critics. A senior official with Shultz's party affirmed that the step would cost President Reagan some support in Congress, but that safety and bilateral considerations had persuaded the administration to permit India to buy the spares it needed from US companies in third countries. And if India could not get all the spares it needed, the US administration was prepared to use its executive powers to ensure that it could get them from the US.
Substantial though it was, that initiative does not entirely resolve the Tarapur tangle which has one more chapter, the climax, to be written. India says that since the US failed to honor its commitment to supply fuel for 30 years it can no longer determine how the spent fuel - which can be reprocessed into weapons-grade uranium - is to be used. The US, for its part, maintains that India does not have that leeway, and Shultz made it clear at his press conference Friday that differences persist.
That was not the only time, however, the he found himself admitting to the existence of differences between the two countries. During the visit, both sides affirmed in their statements to one another, both public and private, India and the US are far apart on several key issues ranging from aid and trade to Afghanistan and Indian Ocean security, from the Middle East to the global role of the Soviet Union, from arms supplies to Pakistan to Vietnam, Kampuchea, and China.
This was why official pronouncements on concrete achievements of the visit tended to remain vague - on both sides. Shultz had more than an hour alone with Premier Gandhi and was invited back to an unscheduled tea meeting. But asked to list American priorities in relations with India, an American official said it was to maintain a dialogue with India so that misunderstandings did not occur.
The underlying reality to all this is that Indo-American ties have started out in diplomatic terms from the low of the Nixon years. Since then both countries have moved a long way, India having realized that its close attachment to the Soviet Union was costing it in terms of development, technology and diplomatic elbow room.
Much more important ties have, therefore, been recorded in areas which do not require either government to take hard, public postures. India's willingness to open its economic borders to foreign investment and know-how has revived American business interest and the US remains one of India's most important trade partners. Though still insignificant in global terms, there is a calculated effort to bring into India American technology and investment in key areas. Behind the scenes, cooperation in scientific, cultural, and educational fields has come to assume an importance that political differences cannot decry.
Dramatic progress is impossible in any of these areas, but there is a steady if slow movement. Their significance is that for the first time in recent years an effort is being made to give the Indo-American relationship a firmer basis which veers away from the differing political perceptions that exist on both sides.