A leading Wall Street economist warned today that the nation could be plunged into a depression if the Federal Reserve Board tightens monetary policy again, sending interest rates back up.

Albert M. Wojnilower, chief economist at First Boston Corp., also said that the combination of massive business debt and a hesitancy on the part of major banks to continue corporate lending could block the economic recovery that administration officials say is underway.

"It is no longer altogether certain that a moderate business upturn can provide enough lift to forestall a cascading of bankruptcies," Wojnilower said in an address to executives attending a business outlook meeting sponsored by the Conference Board, a private research group.

Wojnilower's remarks on the possibility of a depression came in response to a question. "If we revert to the kind of monetary policy that prevailed prior to midyear, there will be a depression sooner than later," he responded. Wojnilower's Aug. 16 prediction that interest rates next year are likely to be "noticably lower" for high-quality investments helped prompt the ongoing stock market rally.

Until then, Wojnilower and Salomon Brothers Inc. economist Henry Kaufman had been predicting that interest rates were likely to remain high.

Stock market experts suggested today that Wojnilower's remarks were likely to add to the economic and political pressure on the Fed to maintain an easier policy toward the growth of the money supply, a key factor in the market's recent boom. The stock market rally continued today as the Dow Jones Industrial Average jumped by more than 18 points, hitting its highest closing mark in more than 13 months.

But there was little indication from economists and executives attending today's economic parlay that they had yet felt the effects of the predicted recovery. In fact, Albert T. Sommers, the Conference Board's chief economist, said that he does not expect the economic recovery to begin until late this year.

And at a policy conference here run by The Securities Group, a merchant bank, several academic economists agreed that a recovery this year is likely to be slow and limited. "I don't think it's going to be very vigorous," said one, Stephen Goldfeld, chairman of the Princeton University economics department. "Nobody will be very happy with it."