Dunfey Hotels, a rapidly expanding lodging chain owned by Aer Lingus, the Irish airline, plans to take over operation of Washington's Shoreham Americana hotel shortly after the first of the year.

Dunfey will manage the hotel and will be a partner in a group, headed by New York real estate magnate William Zeckendorf Jr., that is buying the Shoreham, chain president John P. Dunfey said yesterday.

The Zeckendorf group is expected to complete purchase of the Shoreham on Monday.

Zeckendorf and his partners reportedly are paying $35 million for the Shoreham, which is now owned by Lester Meilman, a Chicago real estate investor who heads a company called MAT Associates.

Dunfey said another $5 million will be spent -- starting this spring -- to renovate the hotel and $10 million more in improvements is planned over the next few years.

The Shoreham Americana again will be known as the Shoreham, Dunfey said.

The Dunfey management will replace Americana Hotels, a subsidiary of American Airlines, which has operated the Shoreham for several years. American is cutting back its hotel operations.

Zeckendorf has not identified his partners in the Shoreham purchase. He said the group is the same one that earlier this year purchased the Statler Hilton in New York, which Dunfey also will manage.

Started as a family hotel company in New Hampshire, Dunfey now operates 22 hotels in three divisons. Dunfey is the largest Sheraton hotels franchise operator, with 12 Sheratons. Its biggest properties are known as Dunfey Hotels and its more luxurious facilities operate as Dunfey Classic Hotels.

The Shoreham, Dunfey said, will be part of the classic hotel group and will be upgraded to shift its emphasis away from large conventions toward the higher price business and embassy markets.

The Shoreham is the fourth hotel acquired by Dunfey this year.

The company specializes in upgrading existing hotels. Its properties include the Parker House in Boston, the Ambassador East in Chicago and Berkshire Place in New York, which recently was converted from an economy hotel to a luxury facility.

Dunfey has been eyeing the Washington area for six or seven years, the company president said. The firm was one of the unsuccessful bidders for the Willard Hotel on Pennsylvania Avenue and also tried to buy the Mayflower Hotel on Connecticut Avenue.

Expansion of the Dunfey chain begain when the family company was acquired by Aetna Life and Casualty Co. in 1971. Aetna sold the chain to Aer Lingus in 1976 and accelerated its growth.

The Dunfey president is a prominent New Hampshire Democrat who recently was appointed to a federal commission to establish a "peace academy" to train diplomats. Another Dunfey brother is on the facilities committee for next year's Democratic National Convention in New York and the Dunfey-operated Statler will be the party's headquarters for the convention.

Plans for the Shoreham include demolition of the present motor hotel overlooking Rock Creek Parkway. Zeckendorf has said he hopes to build luxury condominiums on that part of the Shoreham's 11.5 acre site.

Dunfey said his firm also is considering turning one wing of the Shoreham into a premium project with higher room rates, fancier quarters improved facilites, and probably a separate identity, such as The Shoreham Towers.

With 800 rooms, the Shoreham now is Washington's fourth largest hotel -- after the Washington Hilton, the Hyatt Regency and the Sheraton Park. Demolition of the motor hotel will take away about 150 rooms from the project.