Nurses at Prince William Hospital in Manassas are preparing to strike Thursday in what may be the first such action by registered nurses in Virginia.

The nurses, who were unionized in December 1980 and have been pressing ever since for a contract with better staffing, pay, and working conditions, are not strong enough to force a shutdown of the 154-bed hospital, according to both sides.

Nonetheless, negotiations have collapsed, the two sides are speaking of one another in the most acrimonious terms and both the hospital's attorney and its chief administrator are out of town.

The nurses, if they do strike at 7 a.m. Thursday as scheduled, would be breaking a pattern in Virginia, a right-to-work state where strikes by professionals have been extremely rare. Virginia's right-to-work law bars compulsory membership in unions, a provision that many labor leaders say has inhibited the growth of organized labor.

The union represents all the nurses in the hospital, but it does not count all of them as members. Therefore, the extent of the strike Thursday, if it does occur, is in dispute.

David R. Cromer, assistant director of organizing for the Service Employes International Union, said the strike would create a "tough situation for the hospital," although it would not force a shutdown.

But Joel I. Keiler, the hospital's attorney and chief negotiator, says 40 extra nurses have been enlisted and that service will be maintained at 100 percent.

"It will be a dangerous situation," Cromer declared. "They'll have new and untrained people at work -- much more dangerous than the PATCO situation" in which 12,000 air traffic controllers are out on strike.

About 10 articles in the proposed contract remain unresolved, and the two sides are far apart. At the last bargaining session, about two weeks ago, the Prince William Healthcare Professionals, Local 724 of the Service Employes International Union, which represents the hospital's 130 nurses, told the hospital it intended to strike Aug. 13. The strike notice was the last official communication between the two sides.

At issue in the contract dispute are wages, staffing, and certain benefits. The nurses are seeking a pay increase of about 6.2 percent, in addition to a considerable sum in back wages, or a straight $1.70 per hour raise across the board. The hospital management has offered a 66-cent across-the-board hourly raise, plus 5.4 percent at the time the contract is signed, and another 3 percent in September.

The average salary for nurses at the hospital is about $17,000, according to Kenneth B. Swenson, assistant administrator at the hospital.

Cromer, who has been representing the nurses union at the bargaining table, said he thinks the hospital is trying to break the union. He said he thinks the hospital will "tough it out" once a strike is under way until the union buckles.

Although he acknowledged that the Prince William Hospital nurses do not make as much as nurses in the District of Columbia, Swenson said he thought they "had a pretty good wage base" and a sizeable benefit package. He declined to elaborate on the other contract issues.

The nurses say they are also seeking from the hospital a "float pool" of seven nurses that would be used on a day-to-day basis to fill in where needed around the hospital. The nurses charge that the hospital has had severe understaffing problems.

The hospital says, on the other hand, that there are plenty of nurses at work now, and the float pool the nurses are demanding is not needed. Keiler said that staffing for registered nurses was up 13 percent from April 1980, and that staffing "isn't an issue."

Baumler charged that most of the hiring of nurses has been done in the last two months in response to union pressure to beef up staffing.

Swenson acknowledged that a lot of nurses have been hired recently, but denied that it had anything to do with the union's demands or its threat to strike.

Swenson also said he could not remember if the hospital has been understaffed in the past, as the nurses contend. But Keiler, the hospital attorney, said that things "were a little tight" until about a year ago.