While the nation's financial system appears poised for a number of combinations of major firms, foreign companies, especially banks, have been stalking the U.S. market with growing interest.

About 165 foreign banks have nearly 350 offices in the United States. Foreign banks accountd for about 12 percent of the business loans in this country last year.

Much to the chagrin of domestic banks, many foreign banks do their banking business legally in more than one state."There are 42 foreign banks operating in three or more states -- a privilege denied to Citibank," said Walter Wriston, chairman of the bank's parent Citicorp.

In addition to having their own offices in the United States, many foreign banks are buying U.S financial institutions.

Hong Kong & Shanghai Banking Corp. owns a 51 percent chunk of Marine Midland Bank in New York. National Westminister Bank bought the National Bank of North America. A Netherlands bank bought Chicago's LaSalle National Bank. Midland Bank Ltd. is in the process of acquiring the big California bank Crocker National.

According to Wriston, six of the 10 biggest banks in California are owned by foreigners.

James Balog, senior executive vice president of the brokerage firm Drexel Burnham Lambert Inc., in Wall Street. Europeans will not be interested in the big, mass-market securities firms like Bache of Shearson Loeb Rhoades. Balog said many foreign banks are interested in an investment banking presence in the United States, however.

Investment banking -- the underwriting of securities and debt issues for companies and governments -- is separated from commercial banking in the United States, although in most other countries (Italy is the major exception) commercial banking and investment banking are meshed.

Foreigners already have stakes in Wall Street. Dillon, Read, which was just purchased by the big construction moguls, the Bechtel family of San Francisco, has been partially owned by a Swedish bank. Balog's own firm is partially owned by the big Belgian financial conglomerate Groupe Bruxelles Lambert.

Balog said more middle-sized Wall Street firms are likely to be plucked off by foreign interests who want an "investment bank presence rather than a deposit collector on every corner. They want a source of business rather than a source of funds."