RICHMOND -- Gov. Tim Kaine said Wednesday he called a special session of the General Assembly to respond to a recent U.S. Supreme Court ruling that could jeopardize prosecutions of some criminal cases in Virginia.

Kaine said he will call lawmakers into session on Aug. 19 to consider changes to state laws dealing with the use of forensic evidence. The Supreme Court ruled last month in a Massachusetts case that prosecutors must present a forensic scientist as a witness when introducing lab reports as evidence. Virginia law puts the burden on defendants to subpoena scientists in order to challenge lab reports.

"The decision by the court caught a lot of states by surprise," Kaine said in a news conference.

Though Virginia's law is under review by the Supreme Court, Kaine said the ruling in Melendez-Diaz v. Massachusetts would require state scientists to testify in many more cases than they do now. Prosecutors and lawmakers from around the state also have raised concerns about the ruling, warning that it could lead to widespread dismissals of drug and drunken driving cases because lab technicians would not be available to testify.

Kaine said state officials will respond to the court's ruling with a combination of administrative and statutory changes and by releasing state contingency funds to ensure that scientists can testify as needed.

"We believed initially that we could take care of this through some administrative changes to court rules and procedure, but we've concluded that that would still leave some questions and that statutory changes are important and they're important to make promptly," Kaine said.

The board of the Virginia Association of Commonwealth's Attorneys had urged Kaine to call a special session, raising concerns that the June 25 Supreme Court ruling could jeopardize drug and drunken driving prosecutions and other cases involving lab evidence.

"Given the significant impact on the Division of Forensic Science and on pending criminal trials, the governor made the responsible decision to seek prompt legislative action," said Botetourt County Commonwealth's Attorney Joel Branscom, the association's president.

The Virginia Department of Forensic Science has about 160 employees working in four labs statewide. It handled nearly 60,000 cases last year.

"If anyone could tell you what the real-world impact will be, they are only guessing," said Pete Marone, the department's director. "I think prosecutors and judges have the most difficult challenges. We test evidence, and we'll keep on testing evidence."

Prosecutors in the Roanoke and New River valleys have not encountered significant problems because of the ruling but said it could create problems in future cases.

"I am very glad that they are going to address this," said Cliff Hapgood, Franklin County commonwealth's attorney. "It has the potential to make it very difficult to prosecute" these cases.

Roanoke Commonwealth's Attorney Donald Caldwell said the ruling was not having a large effect on his office but is "truly going to be a logistics pain" if lab technicians must travel from court to court to testify. Caldwell said he hopes the ruling leads to wider application of video or teleconferencing technology to accommodate testimony from scientists.

Republican attorney general candidate Ken Cuccinelli, a state senator from Fairfax County, suggested that Virginia can conform its law to so-called "notice-waiver" statutes on the books in three states. Under such a law, prosecutors notify defendants of their intent to introduce lab reports. If the defense objects, prosecutors must make the scientist who prepared the report available to testify.

Kaine called the session for Aug. 19 because members of three General Assembly money committees already have a joint meeting scheduled to hear Kaine deliver an update on state revenues. Kaine said his administration will work with lawmakers from both houses and both parties to craft legislation.

House Majority Leader Morgan Griffith, R-Salem, said legislative committees likely will meet before Aug. 19 to hear testimony and mark up legislation. Griffith is chairman of the criminal laws subcommittee of the House Courts of Justice Committee, making him a key player in the special session.

"I think it's more complicated than even the governor realizes, and while I believe we can do it one day, it's going to take a lot of work by the courts committees prior to that date," Griffith said.

Staff writers Mike Gangloff and Shawna Morrison contributed to this report.