WASHINGTON -- Barack Obama's campaign has concerns about the possibility of Florida and Michigan holding a Democratic presidential vote by mail, the candidate's senior strategist said Tuesday.

Democratic leaders in the two states are considering a mail-in election to allocate delegates to the Democratic National Convention between Obama and Hillary Rodham Clinton. The Democratic National Committee will not seat delegates chosen by primaries held in January, earlier than allowed under party rules.

David Axelrod, Obama's senior strategist, told reporters Tuesday that the campaign is reserving final judgment until a plan is offered.

"But obviously there are concerns about a mail-in vote. I mean, there are concerns about eligibility, ballot security," he said during a conference call. "The state of Oregon has mail-in voting, and it took them more than a decade to perfect it to the point where they felt that they could run a statewide campaign through mail-in votes. And now we're going to turn this process over to parties within the states to run on with a matter of weeks to prepare."

Clinton won both primaries, but all the Democratic candidates had agreed not to participate since the contests were held in violation of party rules. The states moved their primary dates earlier on the calendar to protest rules that favored Iowa and New Hampshire. But the tight race between Clinton and Obama is creating interest in do-over contests that would count toward the nomination.

DNC Chairman Howard Dean expressed support for a mail-in primary during a television interview Sunday.

"Every voter gets a ballot in the mail," Dean said on "Face the Nation" on CBS. "It's comprehensive, you get to vote if you're in Iraq or in a nursing home. It's not a bad way to do this."

Clinton's campaign did not immediately respond Tuesday to a request for comment. But her top Florida supporter, Sen. Bill Nelson, has been promoting a primary by mail, and his office has been consulting with officials in Oregon about how they handle it.

In Michigan, Sen. Carl Levin told reporters Monday that a "caucus-by-mail" approach appeared to be the only practical way of settling Michigan's delegate dispute. But Levin earlier this week raised concerns of his own.

Two co-chairman of Obama's campaign in Michigan also say they're leery of redoing the primary by mail. They'd prefer that the DNC evenly split Michigan's 128 delegates between Clinton and Obama, who was not on the primary ballot because he didn't want to anger other early voting states.

State Sens. Buzz Thomas and Tupac Hunter, both of Detroit, said they've taken their concerns to Obama's national campaign in Chicago.

"You can't really verify signatures on ballots" in a mail-in election held by the state Democratic Party, state Sen. Buzz Thomas. "I strongly recommend that we do look to splitting Michigan's delegates 50-50 and taking that back to the national party."

Under that scenario, Michigan's 28 superdelegates would still be free to vote however they choose, he said. But the party would save the millions it would cost to hold a do-over election.

"This election is too important to do something that potentially could be fraught with mistakes," Hunter said.