Twenty huge banks and investment firms led by J.P. Morgan hold dominating stock positions in hundreds of the nation's Fortune 500 giant industrial firms, according to a new study by Corporate Data Exchange, a New York-based nonprofit research firm.

Morgan was among the top five stockholders in 104 companies; it was first in 13 of them, such as IBM, American Cyanamid, Gillette, Bethlehem Steel, Eastman Kodak and Sperry, according to CDE's study. atterymarch Financial of Boston was among the first five stockholders in 70 companies, Capital Group of Los Angeles in 61, Prudential Insurance and Teachers Insurance Annuity (TIAA-CREF) in 50 each, Manufacturers Hanover Bank in 48 and Citicorp in 39, according to the study.

The CDE study reveals a high degree of ownership concentration among firms that would otherwise appear to have no connection. CDE President Michael Locker cited the recent takeover battle for Conoco, the big oil firm, as an example.

According to Locker, 34 of the top shareholders of Conoco, including the Capital Group, Manufacturers Hanover Trust, Citicorp and TIAA-CREF, were also among major shareholders of Du Pont. "These 34 investors held 22.89 percent of Conoco and 18.82 percent of Du Pont," said Locker, so it is conceivable that the same shareholders might have decided the fate of the merger on both sides.

Locker said a holding of as little as 5 or 6 percent can often give a stockholder working control of a company's policies. The high degree of concentration shown in the study raises questions about the possibility of collusion among corporate giants as a result of mutual ownership, said Locker.

Here are some of the key findings of the study, according to Locker:

Although Morgan retains its long-held position as "the most influential investor on Wall Street," Locker said it was a surprise that 10 of the 20 top investor groups or banks are located outside New York, including Batterymarch, Capital Group and Delaware Management. Locker said, "These newcomers have emerged by outflanking the banks and insurance companies in attracting pension-fund capital."

Foreign ownership of American corporations "is steadily rising." Foreign banks and investors own big blocks of stock in traditional U.S. companies such as Dan River, Scott Paper, U.S. Industries, Revere Copper, Texasgulf, Stokely Van Camp, W.R. Grace, Standard of Ohio and Standard of California, Kaiser Steel, American Motors, Cities Service and American Bakeries. The Rothschild family controls the Bank of California and New Court Securities, and the pending acquisition of Crocker National Bank by the Midland Bank Group of England "will give an added boost to this trend."

There were 47 different investors that each had at least a half-billion dollars' worth of holdings in one company. Some were familiar names with family holdings in a company founded or developed by the family, such as Ford, Getty, Dow, Du Pont, Hewlett-Packard, Pew (Sun Oil), Keck (Superior Oil), Rockefeller (Exxon) and Mellon (Gulf Oil). Others were less familiar: the Blaustein family held $839 million in Standard Oil of Indiana; Manufacturers Hanover, $646 million in Texaco; Abercrombie family interests, more than $1 billion in Cameron Ironworks, Du Pont family interests, $904 million in General Motors; and first Chicago Corp., more than $1.9 billion in Standard of Indiana.