Fairfax County's voter registrar told a judge yesterday it is "too close to call" whether an anti-tax group has gathered enough valid signatures to force a special referendum on changing the county's form of government.

During the same hearing, Circuit Court Judge Thomas J. Middleton said he hopes to move quickly to decide several key legal questions so that there will be time to hold a special election this summer if such a vote is authorized by the courts. The deadline for scheduling a summer election is July 6.

"I understand the urgency of this issue," Middleton said. "I am acutely aware of the time frame . . . . I'm not going to delay this process one way or the other."

The timing of the election is crucial for Citizens for Sensible Taxation, which has sponsored one of the region's most vigorous rebellions against property taxes. If the group misses the July deadline, it will not achieve one of its prime goals: ousting the sitting Board of Supervisors in November, a year before the board's terms would normally expire.

General Registrar Monica J. Horan, whose office has been reviewing 48,000 signatures submitted by the group, said in an interview that the drive would be "very, very close" to having the necessary 40,884 signatures.

Workers in Horan's office have been reviewing petitions filed by the group six weeks ago, trying to verify how many of the 48,000 signatures belong to registered voters. She said yesterday that after a first review of the petitions, workers validated about 36,500 signatures but discounted "close to 6,000."

That means that about 4,400 of the remaining 5,500 signatures -- many of which Horan said were illegible or presented other verification problems on the first go-around -- need to be identified as belonging to registered voters to force a referendum.

Horan said yesterday she hopes to have a final count by June 15.

Although attorneys for the anti-tax group said they were confident that the petitions were signed by enough voters, they asked Middleton to allow additional petitions to be included in the current count.

Middleton scheduled a hearing on the request for Friday, but both he and Fairfax County Attorney David T. Stitt said that similar requests had been denied in previous referendum drives.

Frederick T. Dykes, of Great Falls, a founder of the anti-tax group, is seeking to change Fairfax's current urban county executive form of government to a county manager form as a way for voters to express their disenchantment with real estate taxes, which have risen more than 30 percent in three years.

The group is hoping to force a referendum in late summer in which voters could decide to change the county's form of government. If the change were approved by voters, the group would hope to elect a new board of supervisors in November.

Because Virginia law does not allow for recall votes or advisory referendums, Dykes said, a referendum to change the form of government was the only way to remove the board. The group's long-term goal is to persuade local and state lawmakers to limit increases in homeowner tax bills to 5 percent a year.

"What we're looking for is a process for taking a vote. That's more important than having the change {in form of government} accomplished," he said.

Asked why the vote could not wait until November 1991, when the board will face reelection, Dykes said, "That is what we've been doing for decades . . . . Somehow we need a bigger hammer to make the point."

Even if the petitions contain the necessary signatures, the courts will have to settle the questions of when a referendum should be held and whether the current supervisors can be unseated.

Many legal observers -- including Virginia Attorney General Mary Sue Terry and attorneys for Fairfax -- believe that the board cannot legally have its term shortened by a change in government.

In addition, the courts must decide whether the petition effort will be limited by a new Virginia law effectively allowing Fairfax voters to change their form of government only during a November general election.

The new law goes into effect July 1. Because a vote on the proposed referendum cannot be held by then, Fairfax attorneys and Terry believe it must be held in November at the earliest.

Dykes's attorneys have argued in court papers that because the petitions were filed in April, before the law took effect, the referendum should not be subject to the new restriction.

Middleton declined yesterday to rule on that and two other procedural matters, saying the issues would not be not "ripe" until Horan has determined whether enough signatures have been filed to force a referendum.

"I'm concerned about rendering legal opinions on matters that may not arise," he said.

Marcia P. Dykes, Frederick's wife and a founder of the anti-tax group, said that many of the concerns raised by county attorneys are groundless and appear designed to "thwart the will of the citizens" by derailing the referendum.

"If they would work as hard to bring in spending as trying to keep us from having this referendum, we'd be in tall clover," she said.