At times, the record room in the Prince William/Manassas Judicial Center resembles a Wall Street office with property buyers and sellers and others searching the archives, their fingers tap dancing on computer terminals.

Three flights down, Prince William County Sheriff Wilson Garrison has to squeeze 25 deputies into an 18-by-12-foot office they call home base. Commonwealth's Attorney Paul B. Ebert has converted two conference rooms into offices and has cast his eye on a supply room.

Just three years after moving into the nearly $10 million judicial center, county officials are calling for a multimillion-dollar expansion.

The four-story center, a brick-faced, L-shaped building that still looks and smells new, houses about 160 people as well as the general district and circuit courts, the commonwealth's attorney's and sheriff's offices, and juvenile court support services.

The space crunch, which was not entirely unexpected, is what can happen when a locality's population races past its government's ability to provide services. And it is what can result when the willingness to incur debt does not increase as fast as the influx of residents.

"The growth in the county has met and surpassed predictions," said Lon Farris, chairman of the county bar association's courthouse committee. "And if the pace continues, the courthouse is soon going to be bursting at its seams."

In this decade, Prince William's population has leaped by more than 55,000, from 144,703 in 1980 to 200,000 this year, county officials estimate. The number increases by 25,000 when the populations of Manassas and Manassas Park, which are served by the center, are included.

Many of the newcomers who have flocked to the county are young people, a group that social scientists say is likely to be involved in legal disputes or have need of court services. The average age of county residents is 28.

During the 1980s, the number of criminal cases commenced in the judicial center increased by more than 120 percent, from 982 to 2,238, with civil cases mounting as well. Fairfax County, Prince William's larger neighbor to the north, recorded a 26.4 percent increase in criminal cases during the same time frame.

The record room, which last year ranked behind only Fairfax and Virginia Beach in terms of land records and certificates processed in the state, is already crowded and needs to be expanded, said Circuit Court Clerk Charlton Gnadt. In addition, there is not a spare courtroom, so there is no flexibility in the event of special hearings, he said.

Another area of the judicial center signficantly affected by the pressures of growth is the General District Court, which, officials say, may soon require an additional judge -- who would have no courtroom.

"There are some days when people decide to fight those tickets and you will see standing room only," said Linda Gattis, clerk of General District Court. "We've at times literally spilled out of the door. Once the air conditioner shut down just because there were too many bodies" that created too much heat, she said.

Statistics support Gattis' story. In 1986, the court ranked third in Virginia in terms of traffic cases heard by its judges, according to the Virginia Supreme Court. The locality's three general district judges averaged 19,997 traffic cases --

7,023 above the statewide average and 6,002 cases more than the norm in urban districts.

The population boom also has required the county to increase services that have a direct impact on the judicial center, such as the police force, which has grown from 150 officers in 1980 to 226 last year.

To cope, the Prince William Board of County Supervisors in July formed a committee, composed of representatives from the court and the three affected jurisdictions, to analyze the space crunch. The committee is studying a number of funding options, including general obligation bonds and a lease-purchase agreement under which the county would build additional space and lease part of it to private business.

The group is expected to issue a report this week and if there are no hitches, construction might begin in 1988 on an estimated $4 million expansion of the existing center and construction of a separate building, totaling about 40,000 square feet -- or more than half of the 76,800 square feet now in use.

Many of the court officials interviewed said they knew when they moved into the building -- which was designed so that it could be expanded -- that the space wouldn't last long. Officials were hoping the building would at least be adequate until 1990. If the construction begins by spring of next year, the 1990 deadline could be met, officials say, but in the meantime they are faced with renting space in other buildings or reshuffling offices in the center, which has excess space in some areas.

Fairfax also is planning to expand its facility -- with a $1.2 million addition by April 1989 -- because of a substantial increase in land records and certificates processed, but the county built its five-year-old facility with a substantial amount of extra space for additional courtrooms.

Some ask: "Why did Prince William build a courthouse with space enough for six years?" is money and politics.

Although the bulging population has created an immediate need for millions of dollars for roads, schools and a jail expansion, getting voter approval for such projects has been difficult at best. Just last year, voters turned down a multimillion-dollar bond referendum that included a number of capital improvement projects.

"Nobody got the space they wanted," said Circuit Judge Percy Thornton Jr., who was instrumental in lobbying support for the new center, which, he said, had been talked about since 1957. "We wanted to get unfinished space that would last to the year 2000."

However, funding for the facility was set at a specific level. "You had to take what you could get," Thornton said. "If you can't get the whole loaf, you take half a loaf."

Most people involved with the court system aren't complaining about minor inconveniences, Thornton said, because they can remember having courts strung out in a myriad of buildings in downtown Manassas.

Before funding was allotted for the center, a referendum was held to see if residents would support paying for the center through general obligation bonds. It passed by just 56 votes. A 1978 referendum that included a courthouse, jail and administration building was voted down.

County officials say public mistrust of the supervisors was high and there was debate over whether the judicial center should be in the City of Manassas or the county.

Supervisor Donald E. Kidwell (R-Woodbridge) said the board believed the center's space would be sufficient for the forseeable future and that the funding was adequate. "We didn't anticipate having to do something this quickly," he said.

And as for court officials knowing that there would be immediate space problems, Kidwell said: "Nobody said that then."

The fact was, Kidwell said, there was "no constituency to build a courthouse." And Prince William is a "difficult place to pass referenda" for capital improvements.

To finance the addition and deal with a capital projects deficit, the county will have to be innovative in its fiscal planning, said Larry Hughes, deputy county executive. Constructing the needed buildings will require a "balancing act," said Hughes, who called the capital improvements program "one of the major issues" facing the county.

Success hinges on the county board's long-range planning philosophy and the group's willingness to make difficult decisions, Hughes said.

It might be tough to garner public support for more dollars for larger buildings to accommodate future growth, Hughes said, "but it is also difficult to move into a new building and say 'uh-oh, we don't have room for two departments.'"