LOS ANGELES (AP) _ The $4.2 billion acquisition of the nation's largest food store chain was completed Monday when shareholders of Safeway Stores gave final approval to a merger plan, the company announced.

More than 98 percent of the stockholders voting Monday approved the merger of the company and a holding corporation. The vote came at a special meeting of stockholders representing about 83.2 percent of the outstanding shares of the company's common stock.

As a result of the vote, Safeway has been merged with Safeway Stores Holdings Corp., a corporation formed by the investment firm Kolhberg Kravis Roberts & Co.

Safeway on July 27 agreed to be acquired by Kohlberg Kravis Roberts in a leveraged buyout earlier this year after rejecting a hostile bid from Dart Group Inc., based in Landover, Md.

In a leveraged buyout, the acquiring company pays off debt incurred to make the acquisition with revenue from the target company's operations or the sale of its assets.

Each share of Safeway common stock outstanding at the time of the merger, other than shares held by Safeway, Holdings or their subsidiaries, has been converted into the right to receive a junior subordinated debenture and a pro rata share of warrants.

The debenture, due 2006, is in the principal amount of $61.60 and bears interest at 15 percent through Nov. 24, 1988, and at 14 1/2 percent per annum thereafter.

The warrants are to purchase 4,643,000 shares of common stock of holdings for an aggregate purchase price upon exercise of $17.5 million.

The holding corporation said it would send instructions to stockholders during the next few days regarding the surrender of their Safeway common stock certificates to the First National Bank of Boston, the exchange agent, to make the exchange of Safeway stock certificates for the appropriate amount of debentures and warrants.

T