With spending for defense, farm price supports, unemployment benefits and Medicare running lower than expected, the federal budget deficit for fiscal 1983 could turn out to be $200 billion or less, some $10 billion below the Reagan administration's mid-July estimate.

Officials at the Congressional Budget Office and a number of private forecasters estimating the lower spending figures for the fiscal year ending next week say a variety of factors are responsible, including lower fuel costs at the Department of Defense and the summer-long drought that has induced many farmers to sell grain and pay off outstanding government loans.

Outlays probably will turn out to be $800 billion, compared with an administration estimate of $809.8 billion, the sources say. The recent sale by the government of Chrysler Corp. stock warrants netted $311 million, while the Export-Import Bank received an unexpected repayment of $400 million from the Iranian government. That $711 million is shown as receipts that lower outlays.

Meanwhile, the economic recovery has so far produced no surge in revenues, which are still pegged close to $600 billion.

At the level of $200 billion, the deficit will still be nearly twice the size of the $110.6 billion gap between spending and receipts in 1982. Forecasts for coming years indicate the red ink will remain in the $200 billion range or higher unless Congress and the president take new steps to cut spending or raise taxes.

The precise meaning of such large federal deficits for the economy is extraordinarily difficult to pin down. A number of analysts believe the deficits will lead to a clash between fiscal and monetary policy beginning next year.

The long-standing dispute on this point between the Treasury Department and the Council of Economic Advisers re-emerged last week as Treasury Secretary Donald T. Regan again declared that there is no necessary connection between deficits and interest rates and CEA Chairman Martin S. Feldstein said the need to finance the deficits will keep interest rates unusually high compared to inflation.

In the strictest sense, those two positions are not incompatible, since Feldstein stressed the effect on real interest rates while Regan talked in terms of actual interest rates. But Regan's speech as a whole gave no indication that he thinks that the large deficits represent any risk to the economy at all, except to the extent that they mean the public sector is larger than he considers desirable.

Regan cited a "thorough" Treasury study as evidence that there is no link between high interest rates and deficits. In a recent article in the Quarterly Review of the Federal Reserve Bank of New York, economist James R. Capra of Lehman Bros., formerly manager of the bank's domestic research department, takes issue with the Treasury conclusions.

Capra, and most other economists, do not challenge the study's finding that "deficits have historically not been high at the same time interest rates and inflation rates were high. But," he continues, "this lack of historical or statistical correspondence by no means proves there is no relationship between deficits and these other variables.

"It may mean that the deficits were not big enough to make a difference, or that other policies or economic events were working to offset the effects," Capra explains. "To evaluate the potential effects of the large projected deficits on the economy, simple correlation analysis is insufficient.

"Some model or view of how the economy works is an essential first step. Next is a forecast of the outlook for the economy, together with some assumption about how public policy (especially monetary policy) will respond or choose not to respond to the deficits," he maintains.

Capra follows his own advice and concludes that the deficits "are one of the reasons, although not necessarily the only reason, for what may be constraints on the ability of monetary policy to reduce intermediate- and long-term rates."

As a hypothesis, he suggests that to long-term investors, "large deficits in the midst of a prolonged economic recovery mean one of two things. Either a non-inflationary monetary policy will lead to a confrontation between public and private credit demands that will drive up real interest rates or the Federal Reserve will ultimately accommodate, inflate the money stock, and the economy along with it. Thus, nominal rates will rise."

And there is strong evidence that that hypothesis is correct, Capra declares. Using a forecast showing continued economic growth and the Federal Reserve's publicly stated intentions for growth of total domestic nonfinancial credit for 1983 and 1984, along with a reasonable assumption for 1985, he shows that the deficits will mean problems ahead.

Because of the federal financing needs, Capra says, "funds available for borrowing by the private sector--business, households, and foreigners--would be only about 40 percent or less of the total" funds available under the Federal Reserve policy this year and in 1984 and 1985, if credit expansion is held to the low end of the Fed's 8 1/2 percent to 11 1/2 percent range. The Fed tentatively has decided to lower that range by one-half of a percentage point for 1984 and would be unlikely to increase it for 1985.

Capra says that having only 40 percent of total credit expansion available to the private sector implies "credit market pressures in each year, since private credit and equity comprised much higher fractions of the total--53.8 percent, 69.2 percent, 78.4 percent--in the 1975-77 recovery years.

"Even under the more expansionary policy, where domestic nonfinancial credit was to grow at 11 1/2 percent in 1983 and 11 percent in both 1984 and 1985, funds available for the private sector would be about 55 percent of total funds raised in the credit and equity markets in 1983-85," he calculates.

"In this case, the restrictions on credit growth implied by the monetary targets would not appear to be a problem in 1983--which probably has been the case so far this year--but would become an increasingly serious problem in 1984 and 1985," Capra says.

Those prospective problems, he concludes, are already constraining the Fed's ability to reduce intermediate- and long-term interest rates. Longer term, the deficits will also skew the economy toward more consumption and less investment, a shift that would mean slower growth in productivity.

One of the major goals of the Reagan administration's economic policy, with its focus on tax and spending cuts and economic incentives, has been to increase productivity growth. If Capra's analysis is correct, those policies could turn out to be counterproductive.