A plan to make the presidential battleground of Missouri the first state to allow military voters serving in combat zones such as Iraq to cast their absentee ballots via e-mail is renewing concerns about the security of online voting.

Missouri Secretary of State Matt Blunt, a Republican running for governor, announced the plan Wednesday, saying that "simplifying the voting process for these heroes is the least we can do." The move surprised some computer security experts and voting watchdog groups, who said yesterday that the new rules could lead to Election Day fraud.

Under a deal with the Defense Department, Blunt's office said, Missouri voters serving in designated combat areas will have the option of filling out absentee ballots, scanning them into a computer file and e-mailing the scanned document back to the Defense Department. The department will fax the ballot to local Missouri election officials.

Missouri is the first state to adopt such a system, according to the Defense Department, which sees it as a way to ensure that mail delays do not disenfranchise military voters. "This provides an alternative . . . for citizens who believe the regular absentee ballot cannot be received, voted and returned by mail in time to be counted," said Lt. Col. Ellen Krenke, a department spokeswoman.

In February, the Defense Department dropped a $22 million pilot plan to test Internet voting for 100,000 U.S. military workers and civilians overseas after a panel of scientists identified security concerns. The agency said it could not ensure the legitimacy of votes cast online.

Missouri's system is different, Krenke said, because it is not entirely based on the Internet. The ballots are signed and then scanned before being e-mailed so local election officials will be able to compare voters' signatures to ones on file.

Service members who use the system will forfeit keeping their ballot secret; the Defense Department and county officials will know the candidates chosen. Krenke said the military will use fax numbers to create an audit trail, and all ballots returned to local election officials will contain an official cover sheet. The type of e-mail software will depend on what is available in the field, she said.

The state has not done an independent study of the new system's security, said Blunt spokesman Spence Jackson. "We trust the military," he said.

But Bruce Schneier, a computer security expert on the board of the National Committee for Voting Integrity, said that the public has a right to more details about how the system will work. How will independent observers ensure that the Defense Department does not "lose ballots?" he asked. "There's been no discussion, no audits, no information about how will it prevent phony votes or hacking. Missouri is setting itself up to be the next Florida."

Elliot M. Mincberg, legal director for the People for the American Way Foundation, said he is concerned service members will feel pressured by commanders and colleagues to give up their right to vote in secret. "We are going to look closely at this," he said.