Treasury Undersecretary Beryl Sprinkel warned yesterday that unless the Federal Reserve Board allows money supply growth to expand beyond the 1 percent of the past four months, "it would cause a significant deterioration in economic activity."

In a debate on the economic outlook with Walter Mondale adviser George L. Perry, Sprinkel -- lately pressed into service as a senior economic spokesman for the administration -- made plain that in a second Reagan term, the administration will keep the heat on the Fed to achieve "moderate, stable growth in the money supply."

He said that the limited expansion of the money supply in recent months had brought the Fed close "to the bottom" of the 4 percent to 8 percent growth target it had chosen for this year, "and we would like to see them resume moderate expansion -- to the middle of the range would be fine with us."

Sprinkel and Treasury Secretary Donald T. Regan have made it clear that their scenario for reducing the budget deficit excludes a tax increase, and instead depends heavily on sustaining high economic growth rates combined with budget-cutting.

What isn't clear is whether the Fed will be willing to follow the monetary policy prescribed by Sprinkel and Regan in the absence of a tighter fiscal policy.

Because the post of chairman of the Council of Economic Advisers has been vacant since the resignation this summer of Martin S. Feldstein, Sprinkel has been tapped frequently in the past several weeks as a general spokesman for administration policy.

A Treasury spokesman said Sprinkel had averaged about three speeches a week during October, some of which were arranged by the Reagan-Bush campaign committee. He is scheduled to appear tonight on the PBS television show, "Wall Street Week," to respond to Perry, who made the case for Mondale on that show last week.

In yesterday's debate at American University, Sprinkel argued that the present economic recovery "is no fluke," but the strongest of the post-World War II era, except for the period after the Korean War. He said that signs "bode well" for a continuation of the expansion because investment has been booming, productivity growth had resumed (until mid-1984), and especially because interest rates and inflation are down.

Provided that "the Fed follows moderate policies," Sprinkel said, he is "optimistic that interest rates will continue to decline, on the average, in the months and years ahead."

Perry, an economist on the Brookings Institution staff, agreed that "the prospects for growth are excellent . . . but if the prospects are good, so are the prospects for screwing it up."

He assailed Reagan administration policies of the past four years, saying that "the only good policies are old ones" left over from the Carter administration.

He cited deregulation of the trucking, airline and oil industries, which he said were started under Carter, as well as the former president's appointment of Federal Reserve Chairman Paul A. Volcker, whom he said deserves the main credit for the successful fight against inflation.

The main "bad idea" that Perry ascribed to the Reagan administration is the notion that "we can grow our way out of budget deficits, an idea that never had professional credibility, and doesn't now.

"One of the main ways we can screw up is by not dealing with that problem squarely and promptly," Perry said.

He noted that with a trade deficit running this year at a rate of $150 billion, and huge capital investments from abroad triggered by an overvalued dollar, "we are headed toward becoming the world's biggest debtor nation. Sprinkel says it's wonderful that people are bringing all this money into the country. But all the earnings from those investments are going to go abroad," the Brookings economist warned.

Sprinkel reiterated the administration's opposition to a tax increase "as an anti-growth, anti-opportunity policy," adding that the president "has made it as clear as it can possibly be made that this will not be the policy of our administration. It would be an absolutely last resort."

Sprinkel acknowledged that the federal budget deficit is a problem, primarily "because expenditures clearly have not been cut to the bone . . . we haven't been able to cut the budget, all we've been able to do is slow the rate of rise in government spending."

The way to deal with the deficit, Sprinkel said yesterday, is to increase economic growth with the help of a stable growth in the money supply, and a cut in the real rate of growth in federal outlays to 1.5 percent a year. With a 4 percent real GNP growth rate, the deficit can be brought down to 1 percent of GNP (from 4.5 percent now) by 1988 or 1989, he contended.