The Justice Department has opened an antitrust investigation of Marriott Corp.'s $149 million purchase of Host International Inc., the two companies disclosed yesterday.

The investigation focuses on the in-flight catering businesses of the two companies, Marriott and Host said in a brief announcement. Although Marriott is the world leader in flight meals to airlines, Host's primary business is in the airport retail and restaurant field. Host has a much smaller in-flight catering business, a Marriott spokesman said.

But the purchase provides Marriott with access to Host's extensive airport kitchen facilities. Host operates bars and shops at 25 airports in the United States, including food and merchandising facilities at Baltimore/Washington International Airport.

A Marriott spokesman said the company received brief notification Tuesday of the government inquiry and said the company has not been asked for additional documents related to the Host takeover. "The company does not believe the inquiry will prevent the acquisition from taking place," the spokesman said.

Under federal law, the takeover could not take place until the close of a waiting period designed to permit study of the transaction by either the Justice Department or the Federal Trade Commission. Host stockholders are scheduled to vote on the takeover agreement March 2.

Marriott's contract food services business, second only to the company's hotel operations, produced sales of $529 million and profits of almost $40 million last year, figures that dwarfed Host's sales of $357 million and profits of $14 million.

In completing the purchase, Marriott agreed in December to pay $31 apiece for all of Host's 4.8 million shares.