Computerized background checks stopped 273 people with mental health problems from buying guns in Virginia over the past two years.

That number could increase significantly, depending on what Gov. Tim Kaine does in the coming days to close a reporting loophole that allowed Seung-Hui Cho to legally purchase the two guns he used to kill 32 people on the Virginia Tech campus.

Virginia includes only the names of people involuntarily committed to a mental facility in a database used to screen potential gun buyers. But a federal law prohibits firearm sales to a larger population, those who have been adjudicated "mentally defective."

Kaine said he reacted with "shock and amazement" when he learned of the loophole that allowed Cho to legally purchase his weapons.

Although a special justice found Cho to be a danger to himself in 2005 and ordered him to receive outpatient mental treatment, the Tech student was not sent to a facility against his will.

As a result, the words "Yes, the transfer is approved" appeared on a computer screen when Cho bought a .22-caliber semiautomatic pistol from an online dealer in February and a 9 mm semi- automatic pistol from a Roanoke gun store in March.

"Virginia is the leader in the nation in reporting this [mental health] data," Kaine said in an interview Thursday. "But this is a particular kind of adjudication that wasn't reported that I think should have been. And we need to clarify that going forward."

Kaine said he and Attorney General Bob McDonnell hope to come up with a "workable fix" to the loophole early next week.

Virginia was the first state in the nation to begin running background checks on gun buyers. The checks, which apply to federally licensed gun dealers but not private sellers, are supposed to catch felony convictions, misdemeanors involving domestic violence, mental health commitments, protective orders and other prohibitors to gun ownership.

Of the more than 3 million records included in the database, 80,495 are for involuntary commitments to a mental facility.

With the database, Virginia was able to prevent 250 gun sales to people with mental health problems in 2005 and 2006 and another 23 in the first three months of this year, according to Donna Tate, manager of the state police Firearms Transaction Center.

With details of what Kaine called a "workable fix" yet to be announced, it's hard to say how many more sales might be blocked in the future.

"If people are really slipping through the cracks, who knows how large the numbers could be," said Sam Hoover, a staff attorney for the Legal Community Against Violence, a California-based law center dedicated to reducing gun violence.

About 9,500 temporary detentions are issued each year in Virginia for people whose mental problems might pose a risk to themselves or others. More than 30,000 commitment hearings are conducted by special justices annually.

Kaine also said he hopes other states will follow Virginia's lead so that all states are providing the same information to the federal database.

"I hope, in laying out this fix, we can also do some things to encourage other states that are not reporting this information in to do so," Kaine said.

"Because if somebody's blocked for reasons of a mental health history from buying a gun in Virginia, they can go over a state line and buy one in another state that doesn't distribute this information."

Virginia is one of 22 states that report mental health information to either their own database or the federal National Instant Criminal Background Check System, Hoover said.

With different criteria from state to state, and with some states refusing to provide any data on privacy grounds, "mental illness remains significantly under reported," a 2006 study by Hoover's organization found.

"The system is only as good as the information that is put into it, and certain states do it better than other states, and some states don't do it at all," Hoover said.

Kaine is expected to address Virginia's reporting gap for the short term, possibly through use of an executive order, with a more permanent solution to be studied by investigative panels and lawmakers.

"I think Virginia is headed in the right direction," Hoover said. "But obviously someone slipped through the cracks and there were disastrous results" -- a reference to last week's shooting rampage in which Cho killed 32 people in a dormitory and academic building before killing himself as police closed in.

Because computer background checks do not explain at the point of sale why a transaction was denied, area gun dealers were unable to say how many mentally unstable people they might have turned away.

But sellers can stop a sale on their own accord if they sense something is not right, said Leane Anderson, sales manager at Custom Gun Shop in Christiansburg.

"I'm sure that if a person seemed mentally unstable, I would certainly not want anything to do with it," she said.