SAN MATEO — A Bay Area lawmaker wants to change the rules so that state residents can cast an election ballot even if they haven't registered to vote ahead of time.

State Sen. Leland Yee, D-San Francisco, soon plans to propose a new piece of legislation that would allow would-be voters to register at a polling place on the day of an election. They would still have to be eligible to vote, they just wouldn't have to get their registration card into to the registrar's office 15 days before the election.

Yee said the 15-day registration cutoff in California keeps people from voting. A handful of states that have similar laws allowing Election Day registration have seen a noticeable bump in citizens doing their civic duty, he said.

But one critic said the rule could leave the door open for fraud and bring in voters who probably shouldn't be able to cast a ballot.

Under Yee's proposed rule, an unregistered voter would go to the polling station on Election Day and fill out a registration card and a ballot. The vote would be considered a provisional ballot and held until the officials can determine if the person is eligible. For people who don't have the right to vote, such as minors and felons, the ballot would not be counted. But for those who are eligible, the vote would go into the candidate's final tally. This system would prevent "vote early, vote often"-type fraud, Yee said, while allowing people to vote who might otherwise miss the registration deadline.

"People need to participate. People need to vote," he said. "The strength of our democracy depends on a vigorous voting process."

Once a statewide voter database called VoteCal is up and running, the process will become even simpler, Yee said. Those who want to vote would show up at a polling station, have their name entered into the system and would be signed up instantly if eligible, he said. VoteCal is slated to be online by 2012.

But a fellow at the Hoover Institute, a Stanford-based think tank, said same day registration makes voter fraud a lot easier. Citing an example, Bill Whalen said a person could just come to a polling place with phony identification and sign up. He went on to say the provisional ballot system could make for a tortuous recount in the case of a cliff hanger election.

"There have to be certain barriers," Whalen said. "Here I am, sign me up — it's too much."

But getting excited about an election at the last minute is quite common among voters, said San Mateo County Chief Elections Officer Warren Slocum. For whatever reason, people may not be tuned in to what is happening until the very end. Unfortunately, by then they can't get registered to cast a ballot. Keeping people out of the voting process is a bad idea, especially when there is a controlled way to remedy the situation.

"Several states have day-of legislation," Slocum said, referring to Idaho, New Hampshire, Maine, Minnesota, Wisconsin, and Wyoming. "We know from them that it is safe."

Safe or not, Whalen thinks that people who don't pay attention until an election is in its final stages shouldn't be allowed to vote. He added that people who have been following the process all along probably have a better command of the issues and thus will make better choices.

If legislators want to improve turnout, he said, they should make voter registration mandatory for California residents on their 18th birthday or for students at state schools.

"Frankly, if people are waiting until last moment," he said, "they should not be able to vote."