Kuwait, the second-largest oil producer in the Orgainization of Petroleum Exporting Countries, has amassed huge blocks of American securites now worth close to $7 billion. And if Kuwait's American adviser on U.S. securities, Citibank, has its way, the amount could swell to roughly $8 billion before the end of the year.

Confidential documents have been obtained by the Chicago Tribune that detail for the very first time an OPEC nation's broad-based holdings in the United States. They dispute the repeated statements of Treasury and other government officials that OPEC's petro-billions invested in the United States are going primarily into short-term money market securities, such as Treasury bills.

They also raise serious questions as to the extent of the equity holdings of the other 12 OPEC producers, including Saudi Arabia, the biggest oil exporter of them all.

The documents reveal that Kuwait -- which had petro revenues last year of $18.6 billion -- has acquired from 1 percent to over 2 percent of the common shares of a slew of the biggest U.S. companies including Dow Chemical, J. C. Penney, McDonald's, Honeywell, Burroughs, General Mills, K mart, Burlington Industries, Ralston Purina, Associated Dry Goods Corp. and Kerr-mcGee.

The documents, which also detail private meetings between Citibank and Kuwaiti officials, reveal that the Opec producer is unhappy with that bank's management of its funds and has threatened to shift its assets to another bank. Essentially, it wants Citibank to trade the equity market more aggressively -- to generate more capital gains.

Considering the Kuwaiti billions in the marketplace, a more aggressive investment strategy -- if adhered to by Citibank -- clearly could be a destructive force. It would add considerable more volatility to an already volatile stock market.

Included in the documents obtained by the Tribune is a complete breakdown of two of the largest Kuwaiti equity accounts managed by Citibank -- the Earmarked and Reserve portfolios (which are detailed in an accompanying chart). The holdings are as of last April 4. Their asset values, though, are based on stock prices as of last December, and stood at $2.47 billion -- about a $317 million increase from the cost of the stocks.

All told, Citibank manages five equity portfolios for Kuwait, which, as of last Nov. 28, carried a market value of approximately $3.7 billion. Another $3.3 billion was in bonds and short-term securities. Plans call for this portfolio, which contains about $440 million of Canadian equities and bonds, to be increased to over $8 billion by December.

To guard the identity of the owner of these equities, some of which are stored in Citibank branches in London and Nassau, Citibank lists the Kuwaiti holdings in a secretly coded "M" account.

An examination of Kuwait's equity holdings in the United States -- which cover the bread-and-butter of corporate America -- shows ownership in 15 U.S. banks. These include interests in Bank of America, Chase Manhattan, Mellon National Corp. and Continental Illinois. Kuwaiths biggest interest in a bank -- 2.2 percent -- is held in the Pittsburgh National Bank.

The Kuwaitis also are using their surging oil revenues to buy up sizable chunks of the most important U.S. energy companies. In fact, more than 22 percent of their two biggest portfolios is centered in oil and oil-service companies. Included are over 1.8 million shares of Atlantic Richfield, more than 1.2 million shares of Phillips Petroleum and over 1 million shares of Conoco.

Ma Bell is another favorite of the Kuwaitis. The Citibank documents show they shelled out nearly $100 million to buy close to 1.8 million shares of American Telephone & Telegraph.

Peter Vermilye, Citibank's chief investment officer, declined to talk about the Kuwaiti investments. "We don't talk about our clients' affairs, including Kuwait, and there's no more sensitive account than that one," he said.

Vermilye's concern is understandable since Kuwait -- by the virtue of its assets -- is undoubtedly one of the biggest, if not the biggest, of Citibank's investment accounts. Its total holdings with Citibank -- which is not its only adviser on U.S. investments -- probably place it among the top five mutual funds in the country (excluding money market funds).

One Citibank memo, focusing on the size of Kuwait's investments for the 12 months ending June 30, 1980, notes the following:

A total of almost $1.25 billion of interests and dividends was earned in the past year.

Nearly $33 billion of funds were transferred in and out of accounts.

More than $100 billion of securities transactions were completed during the past year.

These add up to huge management fees from Kuwait, as does its rapid acceleration of U.S. investments, which amounted to only $540 million at the end of 1974.

The greatly accelerated U.S. equity purchases by Kuwait -- and that's only one OpecY member -- again raises the obvious question of whether there's a genuine danger of the oil-exporting nations' gaining control, or, at the very least, a strong influence, over some of the leading U.S. companies.

Paul Erdman, author of "The Crash of '79", and an expert on Mideast affairs, views the Kuwaiti investments as positve. Even though the Kuwaitis are insisting on aggressive trading, they're still making a long-term bet on corporate United States, he said. "And the fact they're working with Citibank, rather than through a Swiss account or a hot-shot Caribbean bank, shows they're being responsible." He said he expects Kuwait always to stay below the 5 percent level in individual U.S. equity investments, so as to avoid making a public announcement.

Acquiring of a position of 5 percent, or more, of a publicly owned company's shares requires a public filing with the Securities and Exchange Commission. s

Erdman's lack of concern is not shared by Rep. Benjamin Rosenthal (D-n.y.), chairman of the Commerce, Consumer and Monetary Affairs subcommittee, which held hearings in 1979 on foreign investments in the United States.

"I'm deeply concerned about OPEC investments in the United States," said Rosenthal, whose committee will resume hearings in July. "The Treasury's data collection is absolutely inadequate," he said. "We could have OPEC countries buying up huge pieces of America without anyone knowing it . . . and there's nothing to arrest it. It's frightening."

Rosenthal said he plans to push for new laws to require that every foreign investment in the United States -- regardless of how small -- be duly reported to both the Treaury Department and the Department of Commerce.

"We need an intelligent inventory of the amount of U.S. assets that are being acquired abroad," he said. "Foreign investments may be good for us -- but not if they lead to foreign domination."