Although foreign competition has forced layoffs of many American steelworkers, at least $133 million in U.S. steelwork pension funds are invested in banks which made massive loans in the last few years to help modernize the Japanese steel industry.

That is one of the more intriguing findings of a new study released by Corporate Data Exchange, a nonprofit organization which has pioneered in compiling information about corporate ownership and holdings. The project was financed by the World Council of Churches and the Shalan Foundation.

CDE concludes in the study -- involving the holdings of the nation's biggest banking and finance companies as of early 1979 -- that financial power in the United States is becoming concentrated increasingly in huge money-center banks like Citicorp, Chase Manhttan and J.P. Morgan.

These banks themselves are increasingly interlocked through cross-holdings, focusing decision-making in even fewer hands, CDE contends.

The study contains some interesting statistics on the interrelationships of these companies:

Many banks and finance companies own and control big blocks of their own stock, sometimes through employe pension funds, thereby allowing managers of the bank or finance company to operate with less outside stockholder control than might otherwise be the case.

For example, Mellon National Corp. holds nearly 24 percent of its own stock. Sears Roebuck, a huge financial institution (as well as retail chain) through its insurance and bankholdings, controls 21 percent of its own stock, chiefly in the form of investments in Sears stock by the company pension plan. CleveTrust controls over 26 percent of its own stock. For Riggs National the figure is 10.3 percent; for United Virginia Bankshares, 12.3 percent.

Many of the giant nationally known banks -- Citicorp., Chase Manhattan, J.P. Morgan -- hold substantial blocks of stock in each other, thereby giving them some hold on their competitors.

Thus, according to CDE, J.P. Morgan and Co. controls the biggest block of shares (4.11 percent) in Citicorp. and the second biggest in Manufacturers Hanover, Bankers Trust and BankAmerica. CitiCorp., in turn, is the fourth biggest holder of shares in J.P. Morgan, the second biggest in First Chicago and the third biggest in BankAmerica. Each of the 11 biggest banks located in the nation's money centers controls substantial blocks of stock in the others.

Many of the giant nationally giants also are big shareholders in smaller banks and financial institutions. Morgan, to take one of the institutions with very broad holdings of this type, is one of the top five stockholders in 31 other financial companies, and this includes not only its stock in brother giants but in some slightly smaller institutions like connecticut General Insurance, Crum and Forster, Marine Midland Bank, Merrill Lynch, Sears Roebuck, Avco, American Express and Mercantile Texas.

Some employe pension funds, like the U.S. Steel pension holdings and the TIAA-CREF holdings (TIAA-CREF is the college teachers' pension fund), hold huge blocks of stock in some of the nation's biggest financial institutions, giving them a substantial voting voice in the affairs of these institutions.

Thus, U.S. Steel through its U.S. Steel and Carnegie Pension Trust, is the biggest single shareholder in Maryland National Bank with 4.89 percent. Moreover, it is in the top five in 35 other institutions, like Southeast Banking, Connecticut General Insurance, TransAmerica, Aetna Life and Casualty and United Virginia Bankshares.

Family interests -- the Mellons, the Rockefellers, the Rothschilds -- still are very big in some banks. Thus, according to CDE, Mellon family interests control 18 percent of Mellon National Bank and by far the biggest block of actual voting shares.

Rothschild family interests control nearly one-third of Bancal Tri-State; the Sid Richardson family of Texas controls 9 percent of Texan American Bankshares. Compared with these, the Rockefeller family interest in Chase Manhattan (2.4 percent) is relatively small though it controls the biggest block of voting shares.

In recent years there has been heavy foreign investment in U.S. financial institutions: Hong Kong and Shanghai Banking obtained more than 51 percent control of Marine Midland Banks in 1980; a Spanish Bank bought about one-seventh control of the Bank of virginia in 1979; an Italian group bought about an eighth of Lehman Bros. Kuhn Loeb; an internatinal group called Compagnie Arabe International d'Investissement bought over 6 percent of Dean Witter Reynolds.