Loans to small businesses during recent months of tight credit have dropped dramatically while loans to large firms have increased, according to data released yesterday by a House Small Business subcommittee.

Small commercial loans given by 48 of the nations' largest banks dropped 40 percent between November and February, and larger loans, usually obtained by big corporations, increased by 13 percent, the data show. The subcommittee is investigating the effects on small businesses of the Federal Reserve Board's tight money policies beginning last October and peaking on March 14.

President Carter vowed in a nationally televised speech in March that small businesses would not bear the brunt of those anti-inflation policies.

Rep. Henry J. Nowak (D-KN.JY.), chairman of the Subcommittee on Access to Equity Capital and Business Opportunities, said small businesses Opportunities, small businesses were having a hard time obtaining financing. But Comptroller of the Currency John G. Heimann said "credit is available to creditworthy small businesses."

"While it is too early to assess the effects of these various policies in small business, there is little evidence to suggest that there has been a differential impact on small versus large enterprises," Heimann said in prepared testimony.

While "recent high interest rates have caused difficulties in some instances" small businesses frequently have been able to cut back on financing needs, Heimann said. He added that financing is not the small business owners' top problem. Inflation, taxes, government regulation and the quality of labor are, he said.

"Generally, policies toward small businesses did not change as monetary policy grew tighter," Heimann said in his statement. "Funds have been aviailable to those willing and able to pay the price."

In contrast, some small business advocates have complained that the tight credit policies have hurt some small firms more severely than larger firms and that the cost and availability of credit are more important to small businesses than to large ones.

According to figures supplied by Nowak, loans of $1,000 to $99,0000 by 48 of the country's largest banks dropped by 40.9 percent from November to February, when the most recent data are available. Loans between $100,000 and $499,000 dropped 24.3 percent, and those characterized as medium -- between $500,000 and $999,000 -- dropped by 8 per cent.

At the same time, loans of $1 million and higher rose 16 percent, the data showed.

Smaller banks also dropped the number of small loans they disbursed, but that decline was smaller than that of the larger banks.

Nowak also said small firms are now being charged higher interest rates than during the previous few months.

"In November 1979 the unusual condition of small loans costing less than large loans existed," Nowak said. "One possible explanation for this inverse relationship might be that a large number of banks were offering special rates to small businesses. However, the Federal Reserve data supplied to us . . . tshow that the price for the smallest, small and medium loans increased while the rate charged on the average large loan decreased."

Heimann said he could not comment on the figures that Nowak supplied because he had not had a chance to study them.