Fairfax County's voter registrar yesterday said an anti-tax group had fallen 778 short of the 40,589 valid signatures needed to force a special referendum on whether to change the county's government.

The group, calling itself Citizens for Sensible Taxation, has hoped to change the form of government in a September referendum. The group says that would enable voters to unseat the current Board of Supervisors in a separate November election, a year before the board's term would normally expire.

"We'll refile," said the group's co-founder Marcia P. Dykes. "We have somewhere between 1,100 and 1,200 on the back burner. We'll put those puppies back in."

But time is running out on the group because of a series of deadlines in state codes. With yesterday's setback, the group cannot get the summer referendum it desires without extraordinary measures, such as a successful appeal to the State Supreme Court.

Unless all legal questions are resolved and enough signatures are validated by July 6, there will be no special election, and the board would serve out its term.

Leaders of the anti-tax group, concerned that they had not accumulated enough valid signatures, sought permission earlier this month to include more signatures in the count. But a Circuit Court judge said the group must resubmit the 39,811 valid signatures with the additional signatures they have accumulated and have the counting process start over again.

"To me, it's totally insane to make {General Registrar Monica J. Horan} go through all those signatures if we can just submit 1,100 or 1,200 more," Dykes said.

The group has the option of appealing that decision to State Supreme Court, but Dykes declined yesterday to say what the group's next move will be. 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.

On April 23, the group filed 48,000 signatures that it had collected over the past year. The group needs signatures from 10 percent of the county's 405,884 registered voters, or 40,589 valid signatures. Horan, whose office spent the last seven weeks trying to verify how many of the 48,000 signatures belong to registered voters, said the group's petitions contain 39,811 valid signatures.

Horan said a breakdown of the invalid signatures shows 4,528 were not registered voters; 2,202 were duplications of names; 1,280 could not be identified; 27 had registered after the group submitted its petitions; and nine were disqualified because one person had signed for two people.

The Great Falls-based group has faced several hurdles in their year-old effort to unseat the board, including court hearings, a dispute over the number of signatures needed and changes in the state law requiring them to file the names before July 1.

Although the group has sought to challenge the current Board of Supervisors in November, Virginia Attorney General Mary Sue Terry has said the Board of Supervisors cannot legally have its term shortened by a change in government.