Union nurses at the Prince William Hospital in Manassas voted yesterday to accept the hospital's contract offer in a move that averted what apparently would have been the first strike by registered nurses in Virginia.

The strike, postponed once, had been scheduled for Aug. 25 by the nurses, members of Local 724 of the Service Employees International Union.

David R. Cromer, an SEIU organizer, declined to give figures for the balloting, but said it was "fairly close." He said there was "quite a struggle" to get the one-year agreement ratified. The union represents about 120 registered nurses at the hospital, but not all are union members.

The wage increases Cromer said the nurses accepted were those previously reported as being offered by management.

The vote ratified a 66-cent-an-hour raise that was put into effect April 1 and a 5.4 percent increase that went into effect June 1. The wage package also includes a 3 percent increase that is to go into effect later.

An assistant hospital administrator said last night he had heard only unofficial reports of the ratification. Joel Keiler, attorney for the hospital, said he had received no word of the vote, but was "not surprised" at reports of ratification.

He said the contract was the same one "they've already turned down three times. There hasn't been anything new proposed by the hospital since some time in the middle of July."

Cromer described union leaders as "quite pleased to have successfully negotiated a contract . . . particularly one which establishes the first registered nurses union in the state of Virginia and the metropolitan Washington D.C. area."