Loudoun County officials said a review of their laws and of plans for a day-laborer center in Herndon has determined that the property straddles the Loudoun border and that the facility would violate the county's zoning ordinance.

Zoning administrator Melinda M. Artman sent a copy of her conclusions to Herndon Town Manager Stephen F. Owen last week. Owen said Friday that town officials were reviewing it.

The Herndon Town Council voted last month to establish a center on a 12-acre site at Sterling and Rock Hill roads where as many as 150 workers could wait to be picked up for construction and other jobs. The center would be operated by Project Hope and Harmony, a social services agency, and would include such offerings as English language classes, a tool-lending service and training for the mostly Hispanic workers. The workers have congregated informally for years in the parking lot of a 7-Eleven a few miles away.

Loudoun County Administrator Kirby M. Bowers sent a letter to the Herndon Town Council before its Aug. 17 meeting warning that the center could also require approval from Loudoun. After the meeting, Bowers asked Artman to make an official determination of whether Loudoun's zoning laws would permit such a center.

"The short answer is no," Artman wrote in a memo dated Tuesday.

Artman said the border between Loudoun County and the Town of Herndon in Fairfax County runs through the former police station on the site. She said about 40 parking spots and the main access road to the property also are in Loudoun. But Owen said the border is just east of the entrance to the property.

Artman said that the property was zoned for single-family residential use and that a day-laborer site would require a special-exception permit. She said the Loudoun County government never issued permits for two other buildings on the property, a recycling center and a public works facility, and never authorized the conversion of the police station from its authorized use as an elementary school.

She said she found other zoning infractions related to those buildings, including insufficient parking for the recycling center, which she said was "almost exclusively" within Loudoun County, and would be sending notices of violations to the Town of Herndon.

Artman's memo advised Herndon officials of two solutions that would put the town in compliance with Loudoun's zoning regulations. The town could contain the center within the Herndon side of the property. But that would require blocking off the portion of the parking lot that falls on the Loudoun side and barring access to the property from Rock Hill Road, which is in Loudoun.

Or, she said, the town could apply for a special-exception permit from Loudoun. But the zoning ordinance says the center would have to be operated by a government agency rather than by a nonprofit organization.

Owen said there were no plans to change the operators of the day-laborer center. He also said that closing the Rock Hill entrance would be "less than ideal" because drivers coming from the east would have to make a U-turn to enter on the Sterling Road side.

He said town officials would consider blocking part of the parking lot. But, he said, "it's not even completely clear" that the border runs as far east into the property as Artman says. He said some maps show that the border falls, at most, several feet past the entrance.

Project Hope and Harmony, the nonprofit organization that has contracted with Herndon to operate the center, has not changed course.

"We are proceeding as normal unless we hear legally that we should do otherwise," said Amy Langrehr, a day-laborer coordinator for the organization. The site could be open within two months, she said.

Two members of the Loudoun County Board of Supervisors who represent areas near the proposed center have said that they oppose the plan and that if it came before the Board of Supervisors for a vote, it would not pass.

"I would be in favor of pursuing all avenues" to keep the center from opening, whether it's "an injunction or whatever," said Supervisor Steven J. Snow (R-Dulles).

Some Loudoun residents have hired a lawyer to help them if the center opens. Their lawyer said they have little recourse unless the users of the center are loud or give them reason to file a nuisance action.

"If people show up and it gets unruly," then they could take action, said Thomas M. Dunlap of Dunlap, Grubb, Weaver & Whitbeck in Leesburg. "But there are a lot of ifs. If they show up and they are orderly and quiet, then that's fine."

He also said a lawsuit filed by the advocacy group Judicial Watch could stall or stop the building of the site. The suit, which lists six Herndon residents as plaintiffs, was filed in Fairfax County Circuit Court on Sept. 1, alleging that the Town Council violated federal and state laws when it approved the center.