Officials of Alexandria Hospital, spurred by long-term financial concerns and a wave of mergers in the medical industry, said last night that they are drafting an "affiliation agreement" with a Washington-based hospital consortium that could link the two by 1990.

George Cook, chairman of Alexandria Hospital's parent corporation, told the corporation members that the agreement with Medlantic Healthcare Group probably would be signed within three months. Although the document leaves several major issues unresolved, Cook said, it signifies that some relationship between the hospital and Medlantic is likely.

"It's not a fait accompli, but something fairly serious is going on," Cook said yesterday. "We've picked the person we want to dance with."

The announcement follows a year of private negotiations between Alexandria Hospital, an independent nonprofit facility, and Medlantic, a nonprofit group that includes Washington Hospital Center and three other D.C. institutions. It also reflects a belief among Alexandria Hospital officials that the facility must find a financial partner to survive in an increasingly competitive field.

In recent years, traditional community hospitals like Alexandria have been squeezed by soaring costs and the emergence of new health care providers, such as for-profit hospitals and health maintenance organizations. Many hospitals have responded by branching into other businesses and banding together to share the expense of sophisticated treatment programs.

In 1986, Alexandria Hospital unveiled plans to supplement its income by building a doctors office complex next to its current building. But neighbors objected to the project, and it was killed last year. A consultant hired by the city recommended that the hospital consider joining forces with a larger facility.

Cook emphasized yesterday that Alexandria Hospital has no current money problems. And he declined to describe the proposed relationship between the hospital and Medlantic as a merger.

"There's a difference between a merger and an affiliation, and what we've got is an affiliation agreement," Cook said. "A merger might mean a combining of administration and creating a totally new entity. An affiliation might mean as little as sharing some facilities and costs. It's an open question how far we'll go."

Cook said one element of the relationship is sure: Alexandria Hospital would continue its practice of treating patients regardless of their ability to pay. The four hospitals that are now members of Medlantic have the same policy.

"We are providing a service to our community and we will continue to provide that service," Cook said. "We would not have selected Medlantic {as a potential partner} if their goals were not the same as ours."

If Alexandria Hospital joins Medlantic it will mark a significant expansion of one of the Washington area's largest and fastest-growing health care businesses.

In addition to its four hospitals, which together have more than 1,400 beds, Medlantic runs a network of walk-in clinics in Maryland, two alcohol and drug treatment centers, a nursing home and a private nurse service.

Alexandria Hospital, which has 414 beds, would be Medlantic's first venture in Northern Virginia, a significant part of the health care market in the Washington area.