Democrats and Republicans here traded accusations of voter fraud, obstruction and intimidation Monday as officials grappled with what is becoming a confused -- and potentially chaotic -- presidential election in this critical battleground state.

As Democrats marched through the downtown streets of the state capital with banners reading "Not This Time!" and chanting "Count every vote," Republicans continued to challenge the eligibility of thousands of newly registered voters. This presented state election officials with the prospect of holding thousands of hearings over the next week to determine who can cast a ballot on Nov. 2.

The continuing legal and bureaucratic uncertainties have heightened fears that Ohio could be on the verge of becoming the next Florida, which could not determine a winner for 36 days after the 2000 election. Polls here show President Bush and Sen. John F. Kerry (D-Mass.) in a statistical dead heat in a state that each needs to win.

"A storm is brewing in Ohio," Columbus Mayor Michael Coleman (D) said Monday. "The day after Election Day, we've got to make sure the sun is shining. By that, I mean each and every vote has to be counted."

Among the looming concerns:

* Republicans have already filed 35,000 challenges to voters' eligibility and are preparing to send recruits into 8,000 polling places next Tuesday to challenge other voters they suspect are not eligible, particularly hundreds of thousands of the newly registered. Democrats are alarmed at the effort, saying it could tie up voting and keep many away from the polls.

* Ohio's voter-registration rolls contain more than 120,000 duplicate names, and an untold number of ineligible voters, such as people who have moved out of the state. A review of the rolls by the Columbus Dispatch even found a murder victim and two suspected terrorists among the eligible.

* Democrats fear that polling places will be inadequately staffed and equipped to handle the crush of voters on Election Day. Rep. Stephanie Tubbs Jones (D-Ohio) said Monday she is concerned that many new voters will not get proper notification from county election boards about where to vote. That is a critical issue in light of a federal appeals court ruling Saturday that voters with provisional ballots -- backup ballots for voters whose names do not appear on the rolls -- must cast them in their own precinct for the votes to count.

In an interview, J. Kenneth Blackwell, Ohio's secretary of state, acknowledged that the state may experience "a few hiccups" in the next eight days, but he dismissed notions of widespread trouble on Nov. 2. "You manage against systemic choking," said Blackwell, whom Democrats have criticized for his dual role as co-chairman of Bush's reelection campaign in Ohio. "I don't think we'll have systemic choking. I don't anticipate the kind of confusion we saw in Florida."

But Democrats, and some election officials as well, say the most potentially disruptive action could be Republican challenges of voters' eligibility filed over the past few days. Although some of the more than 35,000 challenges have been withdrawn or rejected by county officials, about 25,000 are pending.

The Democratic Party and the Kerry-Edwards campaign sent letters Monday to Ohio's 88 county election boards asking them to dismiss the challenges, arguing that they are "unfair" and "arbitrary" and that the Ohio GOP has not provided sufficient evidence under state law that the voters challenged are ineligible.

The rules for challenging voters vary from state to state, and officials nationwide are bracing for an onslaught. In Ohio, the state GOP is drawing on a little-used 1953 law to file its pre-election challenges.

Ohio law states that a party can challenge a voter's eligibility if the challenger has a reasonable doubt that the person is a citizen, is at least 18, or is a legal resident of the state or the county where he shows up to vote. The law also states that local election boards must give voters challenged before Election Day three days' notice before holding a mandatory hearing, no later than two days before the election.

It is not clear, however, how election officials can hold so many hearings, or what they should do after them.

Gwen Dillingham, the Cuyahoga County deputy election director, said 15,000 to 18,000 pre-election challenges have been filed in the Cleveland area, a traditional Democratic stronghold. "I don't know how we're going to find those people to tell them there's a hearing," she said.

Republicans have pointed to what they contend is widespread evidence of fraud in voter registration. Making the rounds on the Sunday talk shows, for instance, Republican National Committee Chairman Ed Gillespie pointed out that in Franklin County, the latest Census shows there are more registered voters than there are age-eligible residents.

But election officials and other experts say there is a reasonable explanation for bloated election rolls that has nothing to do with fraud: The National Voter Registration Act prohibits them from purging voters from the rolls for four years after an initial notification is sent.

"It's unfortunate that there seems to be an assumption that there's fraud behind every problem," said Kay Maxwell, president of the League of Women Voters. "There often is a simple explanation. And we're very concerned that these challenges will intimidate people and keep them from voting."

Some boards, including those in the two counties that are home to the cities of Columbus and Dayton, are tossing out most of the GOP's pre-election challenges because the party made technical errors in filing them.

Of the 4,200 challenges filed in Franklin County, officials have determined that 1,600 are valid. Election Board Director Matthew M. Damschroder, a Republican, said that his board will hold the required hearings on the challenges that remain, but will more than likely keep every voter on the rolls and allow those voters to cast provisional ballots.

One irony of the GOP's challenges in Franklin County and Montgomery County is that many of those challenged are overseas military members -- often Republican supporters -- whose mail cannot be forwarded, officials in both counties said.

Although Ohio law specifies that removing a successfully challenged voter from the rolls is an option, that conflicts with the rules laid out by the National Voter Registration Act. Moreover, local Ohio election boards are bipartisan, with two Republican members and two Democrats, leaving the potential for deadlocks.

Steve Harsman, the Democratic deputy director of the Montgomery County Board of Elections, said he worries that Election Day challenges could create "such congestion at the polls" that people waiting in line will give up and go home.

"The aim of this is to sow confusion and suppress the vote by creating questions about the eligibility of completely eligible voters," said Bob Bauer, one of the chief lawyers for the Democratic National Committee.

Those who marched to Blackwell's office in Columbus appeared to agree. "We cannot forget what happened in Florida," Rep. John Lewis (D-Ga.), a veteran of the civil rights movement of the 1960s, told the crowd. "And it will not happen here."