An Iowa insurance company disclosed yesterday that it has purchased almost 7 percent of the stock in one of Washington's biggest corporations, International Bank.

Life Investors Insurance Co. of America reported it has purchased 590,000 shares of International Bank's common stock for just over $6 million and another 306,000 shares of IB's class A shares for $3.3 million.

The purchases give Life Investors about 7.6 percent of International Bank's Class A stock, 6.8 percent of its common stock and 6.9 percent of the total voting shares.

Life Investors is the only owner of more than 5 percent of International Bank's shares except for the company's chairman, retired Army Gen. George Olmsted, who controls more than 35 percent of the stock.

Olmsted, himself an Iowan, came east after World War II to build a financial empire that now operates in all 50 states and 38 foreign countries.

International Bank is not a bank in the usual sense, but is patterned on European merchant banks, which own shares in many companies. IB's operations include manufacturing, insurance, finance and leasing, foreign banks and a service company that runs the Liberian government's huge ship registration system.

Although Life Investors' purchase of the large block of International Bank stock apparently was a surprise, Olmsted said last night, "I've known them for years. We regard them as very good people."

Olmsted said he hasn't talked with Life Investors executives since last summer. Life Investors hasn't asked to name a member to International Bank's board of directors, the usual preogative of a large investor.

In a report filed with the Securities and Exchange Commission, Life Investors said it bought the IB stock "for investment purposes." The company said it "may acquire additional shares in the future, depending upon market conditions."

Olmsted said he regards the purchases as a friendly move, not an attempt to muscle into the company. Because Olmsted's personal holdings in the company are so large and his expertise in building complex corporate structures is so great, it is considered extremely unlikely that any insurgent could gain a foothold in his company.

The International Bank chairman said he "assumes" Life Investors purchased its IB stock through Securities Corp. of Iowa, one of several stock brokers that makes a market in IB's shares.

Life Investors' reports to the SEC show that the company began purchasing International Bank stock last June and bought the shares in nearly 100 separate transactions since then.

The Iowa firm bought the almost one million shares at market prices ranging from less than $8 to more than $12.50.

The company reported its purchases to the SEC this month after the total passed 5 percent of the outstanding shares of International Bank. Under SEC rules, anyone who acquires more than 5 percent of the stock of a company must make the purchase public.

Based in Cedar Rapids, Life Investors Insurance is a relatively small insurance company that is a subsidiary of Life Investors Inc. The parent company also owns a sporting goods manufacturing company and has investments in other businesses.