Marriott Corp. apparently is retrenching from the dinner-house restaurant business, one of its smallest operations and one of a handful that suffered declining profits in 1978.

According to a terse announcement by Host International Inc. of Santa Monica, Calif., a tentative agreement has been reached for the West Coast firm to acquire "a group" of Marriott's major restaurants.

A Marriott spokeswoman declined to elaborate on the Host announcement, which said only that the restaurants under consideration has sales of $18 million in the year ended last July 31 and are all located in the eastern U.S.

Marriott's dinner-house restaurants operate under the names of Phineas, Joshua Tree, Franklin Stove, Garibaldi's, Hogate's and Port O'Georgetown in the District and its suburbs as well as the Philadelphia area, Connecticut, New Jersey and Long Island.

Host's press release mentioned that the Marriott eating establishments operate under various names but in mentioned only Joshua Tree and Franklin Stove. However, Marriott spokeswoman Barbara Van Blarcum said she could not further identify the restaurants involved.

Marriott has about 20 dinner-house restaurants, profits from which have declined for the past 18 months. The company's fiscal 1978 annual report blamed increased competition, fewer customers and higher advertising and development costs as among factors behind the declining earnings.

Bethesda-based Marriott reported record sales of $1.25 billion for calendar year 1978, mainly from its world-wide hotel, restaurant and airline catering operations.

Host, like Marriott traded on the New York Stock Exchange, said the restaurant takeover is subject to approval of a definitive agreement and ratification by both companies' boards. If approved, the acquisitions would take place about mid-year. No price was disclosed.

With annual sales of about $250 million and 11,000 employes, Host is the nation's largest operator of airline terminal food, beverage and merchandise facilities. The firm also operates specialty restaurants and toll road eating establishments.

In the Washington area, Host operates Casa Maria and Barley Mow. Other restaurants include Jim Dandy Charley Brown and Red Onion. The Marriott restaurants would be placed in Host's specialty restaurant division, which has 37 units in California and D.C.

Separately, Marriott President J. W. Marriott Jr. told security analysts here yesterday that "based on the information we now have," Wall Street froecasts of Marriott earnings in 1979 are "on the conservative side."

Some analysts have been predicting earnings of $1.65 a share compared with $1.43 in 1978, which was up 39 percent from the previous year.

"The momentum of our 43 percent increase in the July 28-Dec. 28 period has continued into the new year and while we cannot predict how long it will continue, we expect the first quarter ending March 23 to be very good in spite of lower restaurant results," Marriott said in a statement distributed by the firm.

In another food services development, Ogden Corp. said it has purchased Wometco Enterprises' area food and refreshment vending operations for an undisclosed price.

Wometco's BaltimoreWashington operations now serve about 40,000 persons a week with annual revenues of about $6 million. Most of the Cheverly-based Wometco business comes from vending machines. The firm serves 147 locations in the region.