WASHINGTON -- The head of a federal voting commission called Tuesday for tougher security measures for electronic voting by the November elections, but said the issue of requiring paper receipts as backup needs further study.

DeForest B. Soaries, chairman of the Election Assistance Commission, said he wants election officials to be able to analyze software source code in the electronic systems they pay for, which some vendors have resisted.

"The increased use of electronic voting devices has created security concerns that the U.S. Election Assistance Commission must address," he said in remarks prepared for delivery at a Maryland conference of election officials.

In an interview before the speech, Soaries said the issue of paper ballots that voters can verify -- perhaps the most-debated aspect of the controversy over electronic voting -- requires more study and that calling for such receipts by November would be unrealistic. He said it was possible the panel would recommend paper ballots in the future.

"If there was unanimity among scholars and scientists on the paper issue it would be a more compelling case," Soaries said. "All of the research, all of the testimony we've received, all the writings that I've read argue for more research."

Some 50 million Americans -- about 30 percent of voters -- are expected to vote electronically on Nov. 2. But concerns about the ATM-like machines have grown since computer scientists began criticizing them as dangerously vulnerable to hackers and mechanical failure.

Many local election officials defend electronic voting as reliable and voter-friendly. But increasingly state and federal policy makers are calling for a "voter verifiable paper ballot" that would create a physical record documenting voter intent.

California's secretary of state is requiring electronic voting machines to produce paper trails by 2006.

Some critics of electronic voting also want vendors to make their software source codes public so they can be widely scrutinized for security flaws.

Soaries said he wasn't prepared to ask software developers to release such proprietary information. But he said he wants the commission to urge vendors to share their source codes with local election officials who use federal money for electronic voting machines.

In his prepared remarks, Soaries said every jurisdiction using electronic voting devices should identify and implement new security measures, and consider options including paper verification, "parallel monitoring" in which the machines are randomly tested on Election Day, cryptography measures and chain of custody and management practices.

He also said vendors of electronic-voting software should submit certified software to the National Institute of Standards and Technology, which would allow election officials to compare software used in elections against an original version.

The four-member, bipartisan commission was created by the Help America Vote Act of 2002. It does not have regulatory authority but is charged with making recommendations for running elections.