WASHINGTON — Only days before millions of Americans cast their ballots, a climate of suspicion hangs over Tuesday’s national elections.

Accusations of partisan dirty tricks and concerns about long voter lines, voting equipment failures and computer errors are rampant, particularly in key battleground states such as Ohio and Colorado, where absentee and provisional ballots could decide a close election.

“Those will be the states that are the most prone to confusion and chaos and contesting if the election is close or within what some people call the ‘margin of litigation,’ ” said Charles Stewart III, a political science professor at the Massachusetts Institute of Technology.

State and local election officials and partisan watchdogs are on high alert for problems, as is the U.S. Department of Justice. All of them plan to post election monitors at potential trouble spots across the country.

The extra preparations will certainly help, but they haven’t stopped reports of phony election workers showing up at people’s homes to collect their absentee ballots or anonymous callers falsely claiming that voters can stay home on Election Day and cast their ballots by phone.

With concerns running high about voter intimidation, voter suppression and poorly trained poll workers, many think that the integrity of the elections – and the officials who run them – has been compromised. Nowhere is that more true than in Ohio, where Republican Secretary of State Jon Husted has drawn the ire of Democrats by limiting the amount of time for early voting.

“It’s highly unfortunate that the rules of the game have become hyper-politicized,” Stewart said. “It sets up a situation that, regardless of who wins the election next Tuesday, the losers, especially the most zealous partisans, will be set up to doubt the legitimacy of the outcome.”

In their national bid to root out voter fraud, True the Vote, a conservative organization, might have hundreds of thousands of poll watchers nationwide. They plan to challenge voters they suspect of casting ballots illegally. This could slow the election process and force challenged voters to cast provisional ballots, which are counted later.

“True the Vote has reported instances of procedural and technical errors occurring in polls that could lend themselves to abuse,” a statement by group founder Catherine Engelbrecht said.

Labor organizations and voting rights groups, such as Common Cause and the Lawyers’ Committee for Civil Rights Under Law, also will have poll watchers making sure that voters aren’t harassed, intimidated or threatened by True the Vote members.

“Our monitors will be monitoring their monitors,” said Judith Browne Dianis, a co-director of the Advancement Project, a national nonpartisan voting-rights organization. “We are going to make sure they’re not engaging in bullying at the polling places.”

The recent high-water mark for voter distrust is the 2000 presidential election, when Florida’s disputed votes and the resulting challenge to the U.S. Supreme Court left the race undecided for several weeks. The high court eventually declared Republican George W. Bush the winner.

Concerns about the 2012 election mushroomed last year as Republican state lawmakers around the country introduced a series of restrictive voting laws that critics claimed would affect minorities, college students and the poor disproportionately. Democrats and civil rights advocates argued that the laws were a less-than-subtle attempt to suppress the votes of some of the party’s strongest supporters.

Federal and state courts in 14 states ended up reversing, weakening or postponing many of the laws’ most contentious provisions, according to the Brennan Center for Justice at New York University School of Law.

In the aftermath of those legal battles, a skeptical electorate wonders whether innocent mistakes, computer glitches and human error by elections workers have a deeper, more sinister intent.

After printing the incorrect election date on voter materials printed in Spanish – but not in English – election officials in Maricopa County, Ariz., made the same mistake a week later with a different document. Once again, the identical English-language materials didn’t have the error.

County Recorder Helen Purcell called the errors regrettable but said accusations that her office was trying to suppress Hispanic voter turnout were “simply a malicious lie.”

Polling by MIT’s Stewart found that roughly 25 percent of voters had doubts about the legitimacy of the 2008 presidential election results. He said recent polls by others suggested that that rate hadn’t changed, nor had there been a large outcry for election revisions as there was after the disputed 2000 election.

“I think what has changed is that this has become a major rallying point for the bases of the parties and for surrogates of the candidates,” he said.

Accusations of partisan politics continue to roil Election Day preparations in Ohio, which many experts think could decide a close presidential race.

Earlier this week, Norman Robbins, the research director at the Northeast Ohio Voter Advocates, a nonpartisan voter-education group, notified Husted’s office that thousands of requests for absentee ballots may have been rejected improperly statewide because of incomplete data checks by local election officials. The checks mistakenly showed that the applicants weren’t registered to vote. Nearly 900 wrongly rejected ballot requests were found in Cuyahoga County alone, Robbins said.

Cuyahoga is Ohio’s most populous county and a Democratic stronghold.

In response, Husted’s office sent a directive to county election offices to try “at least one (of four) additional search criteria” if the name of an absentee ballot applicant doesn’t appear on the list of registered voters.

These kinds of problems are why Stewart thinks Ohio is the wild card in a close presidential election.

“If Ohio is within 2 percent either way,” he said, “then I think we’re in for about a three-week period of high drama over the canvassing of that election.”