The Federal Reserve proposed yesterday that branches and agencies of large foreign banks in the United States be subject to the same reserve requirements as American banks. The regulation is designed to put competition between domestic and international financial institutions on a more equal basis.

The Fed's action comes as Americans are beginning to worry about a foreign bank "invasion." Sen. John Heinz (R-Pa.) recently cited figures showing that the number of foreign banks operating in this country has grown from 66 in 1972 to 189 last year. They now make more than 15 percent of all big U.S. business loans and 30 percent of those loans in New York and California.

Heinz has proposed a six-month ban on takeovers of U.S. banks by overseas financiers. Sen. William Proxmire (D-Wis.) has proposed a longer ban, lasting until April 1981. Meanwhile they have called on President Carter to produce a study by next July on the effect of acquisitions on competition and credit, and on foreign and monetary policy.

Heinz declared yesterday: "The Fed has apparently begun to recognize the problems of foreign takeovers of U.S. banks. However, these actions are only a small first step. The Fed still needs to address the inherent potential for conflicts of interest that can arise from the acquisition of American clearinghouse banks by unspecified foreign interests, the need to establish clear criteria as to what are acceptable institutional or individual buyers and the amount of foreign penetration of domestic markets that is compatible with our national interest."

A Senate Banking Committee staff member said that the Fed's action would not affect plans for moratorium bills. He said he isn't sure that the proposed regulation would create equality so long as foreign branches can issue commercial paper without reserves through thheir parent companies and so long as interstate branching is permitted for them but not for their American competitors.

At a Senate Banking Committee hearing last week. Columbia University researcher Richard B. Cohen raised the specter of a foreign "invasion" when he noted that, during the past two years, acquisitions by European and Asian banks have increased the assets of those banks by 39 percent. Their U.S. assets now exceed $100 billion.

Stated another way, 4 of the top 10 banks in the world were American back in 1972; today, only 3 of the 25 largest commercial banks were U.S. based. "If present trends continue or accelerate, we will lose a significant amount of control of our entire economic system," Heinz warned.

The Fed's prosposal - which affects foreign banks with worldwide assets of more than $1 billion - will allow branches to borrow from the Fed and use its other services in exchange for the reserve requirements. The Fed also will make Eurodollar borrowing subject to the same reserve requirements as U.S. banks. In this way, the Fed will be able to keep better control of monetary policy while Eurodollars and petrodollars continue to flow into this country.

The idea of a moratorium on acquisitions by foreign banks has drawn little support thus far from U.S. bankers. Some, citing the dragged-out case of the Marine Midland-Hongkong & Shanghai Bank merger, maintain that the regulatory process is sufficient to control the situation.

Large New York banks such as Citibank, Morgan Guaranty and Manufacturers Hanover tend to favor competition from abroad so long as they can do so under the same rules.