Martin Feldstein's legacy

White House economic adviser Martin Feldstein returns to Harvard this week against the backdrop of an American economy that looks sunny enough for a summer day in July. What would be unfortunate, however, would be for Feldstein's persistent warnings about budget deficits and interest rates to be forgotten.

Dr. Feldstein's message - indeed, perhaps his lasting legacy from his public tenure as chief economic adviser in the Reagan administration - is that the nation must come to grips with soaring budget deficits. In the no-nonsense Feldstein analysis of economic affairs, deficits push up interest rates as government and private borrowers compete in credit markets. The climbing interest rates, in turn, could, unless checked, abort the recovery.

Partly because of Feldstein's persistence, undeviating through press conferences that often put him at odds with the Oval Office, the White House came around to accepting the argument that short-term action had to be taken to help hold down deficits. The upshot: direct support by President Reagan for the current three-year deficit-reduction, tax-hike package - the so-called ''down payment'' on a larger deficit-reduction agreement that will have to be worked out by the new administration and Congress in 1985.

Economic analysis always operates on a number of parallel tracks in the United States, as Feldstein knows only so well.

There is always a public impression of the economy, based largely on current economic developments. The current trends are certainly strong: unemployment now at 7.1 percent, below what it was at the time of the 1980 presidential election, for example. Factories are humming. Consumers are still fueling recovery. Inflation remains below 5 percent.

But there is another, deeper track of analysis as well. Wall Street tends to watch this level. And what is currently happening on this level raises troubling long-range issues.

Interest rates continue to climb. The US trade imbalance worsens. Auto unions talk about a strike against General Motors later this year. Growth, though apparently easing somewhat, remains strong, prompting concerns about renewed inflation.

It is precisely because of these longer-range concerns that Congress and the White House must follow through as quickly as possible next year on a comprehensive deficit-reduction agreement to ensure that the recovery remains on course.

It seems unlikely that Dr. Feldstein's independent streak will soon be duplicated by another White House economic adviser, particularly in a second Reagan White House, if that proves to be the case.

In many ways Feldstein was an anomaly. Former economic advisers, such as Alan Greenspan and Charles L. Schultze, both of whom were more low-key, will likely prove to be the role models for the office. Greenspan, Schultze, and, going back even further, Walter Heller left a stronger imprint on policy.

A stint in government could add greater clarity to Feldstein's academic research. To his credit, he restored credibility to White House economic analysis in the early 1980s, after the Reagan administration's unhappy early flirtation with ''rosy scenarios.'' And he singled out the importance of going after the budget deficits. That must be reckoned no small legacy.