A Fairfax County schools plan to have neighboring districts, including Loudoun County, help pay for a $90 million renovation of Thomas Jefferson High School for Science and Technology might be illegal, according to Virginia’s attorney general.

Ken Cuccinelli II (R) issued an opinion last week that says Loudoun does not have the legal authority to cover renovation costs for a building outside of its district that it does not lease or partly own. Fairfax officials have asked Loudoun and other counties sending students to the elite magnet school to help pay for part of the renovation, already underway, that includes plans for state-of-the-art science labs and a wave tank for oceanography classes.

Fairfax school officials have said that the county’s taxpayers should not bear the whole burden of the renovation costs when about 20 percent of the school’s 1,815 students come from outside the district. The plan to have counties pitch in — Loudoun would have to pay at least $7.8 million — immediately caused local counties to question whether sending their brightest students to Fairfax still makes sense.

Cuccinelli wrote Friday that state law prohibits Loudoun — which has about 200 students at TJ, as the school is known — from using local taxpayer dollars to pay for infrastructure outside the county unless a contracted agreement specifically called for such payments. Referring to the contract Loudoun has to send students to TJ, Cuccinelli said such capital improvement payments would not be allowed.

Loudoun, Arlington and Prince William counties, and Fairfax and Falls Church cities, pay a per-pupil tuition that covers only operational costs, under current agreements that Fairfax schools spokesman John Torre said are identical. Cuccinelli’s opinion, while narrowly focused on Loudoun, probably would apply to the other districts, as well.

“With this new information from the AG, the superintendent and staff are now evaluating the situation and discussing it with our attorneys,” Arlington County schools Assistant Superintendent Linda Erdos said.

Prince William schools spokesman Philip Kavits said that negotiations between his district and Fairfax regarding the TJ renovation payments are still unresolved.

“Given the opinion, our school board and those from other involved divisions will need to consider appropriate and cost-effective ways to invest in giving some of our students the educational benefits that TJ provides,” Kavits said. “However, it is too soon to speculate on how that might work.”

Torre said Fairfax officials are studying the opinion to determine the best way forward. Ilryong Moon (At Large), chairman of the Fairfax County School Board, said the administration will discuss the attorney general’s opinion with legal counsel.

“Our counselors did a lot of legal research and may disagree,” Moon said, noting that just because Cuccinelli is the attorney general “doesn’t mean he’s always right.”

Fairfax school officials said their renovation proposal has precedent. TJ is one of 19 Virginia Governor’s schools that offer advanced courses. Fairfax officials have said that other governor’s schools in Virginia include fees for building improvements in the cost of tuition.

Loudoun’s contribution for the renovation would be the largest, and the payment of millions of dollars in extra funding has led officials there to investigate other options. In a school system survey of more than 10,000 self-selected Loudoun parents and community members this spring, about 48 percent said they thought the county should slowly phase out participation with TJ.

At the request of the Loudoun School Board, Del. Joe T. May (R-Loudoun) asked Cuccinelli’s office in April for legal guidance.

Cuccinelli responded Friday that “no general statutory authority exists to enable” Loudoun to pay for the TJ renovation. He wrote that a contract that included fixed tuition would allow for renovation costs.

Loudoun School Board member Bill Fox (Leesburg) said after reading the opinion that he believes the school systems can find a way to structure an agreement within the confines of Cuccinelli’s opinion, assuming there is support on the board for continued attendance at the magnet school.

May said the situation is complicated for Loudoun, which is looking to invest in its own science academies.

“Do you spend your education dollars in Loudoun County? Or spend it out of Loudoun County in another county?” May said. “It used to be that Thomas Jefferson was the only game in town, and increasingly that’s no longer the case.”