The medical director of an Alexandria kidney treatment center sued two former colleagues for $7.5 million yesterday, claiming they instigated a "deceitful campaign to steal" his medical practice, according to a suit filed in Alexandria circuit court.

Dr. Raphael J. Osheroff, director of the Northern Virginia Dialysis Center, says an antitrust suit filed against him last year by Drs. Robert E. Greenspan and Steven Tolkan, former clinic staff members, was part of a secret attempt to take over his practice, according to court papers.

Greenspan, Tolkan and four of their patients filed a suit in federal court in Alexandria in which they claimed the clinic's rules violated federal antitrust laws by preventing outside physicians from using life-saving medical equipment it owns. Greenspan and Tolkan's suit said the clinic's owner, National Medical Care Inc. of Boston, opposed the formation of competing centers and said they were prevented from using dialysis machines at the Alexandria clinic after they left their jobs there.

Osheroff, founder of the clinic, remained as director after selling the clinic to National Medical Care.

When U.S. District Judge Oren R. Lewis refused to grant Greenspan and Tolkan access to the clinic, the two physicians dropped the suit.

Now Osheroff, in his suit, says his reputation was seriously damaged by the actions of Greenspan and Tolkan. Osheroff's suit also names as defendants Lawrence E. Rubin, a Silver Spring lawyer, and three other former center employes, saying they assisted Greenspan and Tolkan in their efforts against Osheroff.

While publicly asserting that they were trying to break up a monopoly, Greenspan and Tolkan had actually "embarked upon a deceitful campaign to steal the practice of Dr. Osheroff . . . by taking advantage of Dr. Osheroff during a period in which he was undergoing personal illness," according to court papers.

Greenspan declined comment yesterday, saying he had not yet seen the lawsuit. He said he and Tolkan are practicing together in Alexandria, but lack access to a dialysis machine to treat patients suffering from chronic kidney disorders.