A Boston-based firm that controls 11 of 14 kidney treatment centers in the Washington area has been accused of illegally monopolizing life-saving treatment for hundreds of seriously ill patients.

In a suit filed this week in U.S. District Court in Alexandria, two Northern Virginia physicians and four of their patients claim that the firm, National Medical Care Inc., violates federal antitrust laws by barring outside physicians from using life-saving medical equipment it owns.

Because the doctors, Robert Greenspan and Steven Tolkan, left their jobs at the firm's Alexandria subsidiary last week, they are prevented by company rules from treating patients at any of the three kidney treatment clinics in Northern Virginia, all of which are owned by the Boston firm, according to the suit.

Three times each week, the suit says, patients suffering from advanced kidney disease must be hooked up to dialysis machines for four-hour treatments that remove impurities from their blood. The suit says kidney dialysis centers are highly profitable because 80 percent f the treatment, which costs about $23,000 per year, is federally funded.

According to the suit, National Medical Care, which operated 100 dialysis clinics nationwide, has opposed competing centers, and action the suit calls "a conspiracy to suppress, eliminate and prevent competition."

Attorneys for National Medical Care declined to comment yesterday.

The suit says that last week Greenspan was "arbitrarily" fired from the Alexandria clinic by Dr. Raphael Osheroff, who is also named in the suit. Tolkan, the other physician, quit his job the same day Greenspan was fired.

The four patients, all of whom live in Northern Virginia, may continue to be treated at the clinic by other doctors. But they say they wish to continue to be treated by Greenspan and Tolkan, and are requesting a temporary restraining order to prevent the Alexandria clinic from barring the two physicians.

"The refusal to permit Doctors Greenspan and Tolkan to use chronic dialysis machines . . . which include all the machines in Northern Virginia . . . forces the doctors' patients to relinquish their freedom to choose their physician," the suit says.

The suit also asks that Greenspan and Tolkan be allowed permanent access to the facility and that the two be paid $200,000 each in damages.