Expected record turnout could produce long lines at precincts, which might influence decisions on a proposed constitutional amendment to allow early voting in Maryland.
But long lines are not likely to stifle voter enthusiasm, said Linda Lamone, the state's elections administrator.
"It's almost like this election is a celebration," she said. "The majority of people going to the polls, if they have to stand in line, we think they'll remain positive about it."
Homer Favor, 84, who hasn't missed a presidential election since voting for Harry S. Truman in 1948, predicted "tremendous turnout" from the state's black voters, despite a rainy forecast.
"They sat in the rain to listen to him," the retired Morgan State University economics professor said of foul-weather rallies attended by thousands of Barack Obama supporters during the campaign. "They'll certainly walk in the rain to vote for him."
But James Bell, an Obama volunteer who has already cast an absentee ballot, expressed doubt about turnout from impoverished parts of the city, such as his Harlem Park neighborhood.
"They claim they're voting, but I don't know," said the 73-year-old retired graphics designer. "I still see a lot of negative attitudes ... about voting, about caring about your community."
As an early indication in the level of interest in this election, nearly 227,000 absentee ballots had been requested by Sunday, compared with about 138,000 absentee voters in the 2004 presidential election, officials said.
State officials are projecting a record 85 percent turnout today that could spike to more than 90 percent in Baltimore City and Prince George's County. They have added more equipment and poll workers at key precincts as part of a "line alleviation" plan.
The state elections board also retained a professional call center to answer voter questions, which has fielded tens of thousands of calls in recent days. Meanwhile, a "rumor control" section of the board's Web site seeks to dispel misconceptions.
Elections officials also are reminding people they must vote in the precinct where they reside. In the past, voters who showed up at the wrong polling place could fill out a provisional ballot and their votes for national or statewide candidates were counted.
But a recent ruling by the Maryland Court of Appeals has restricted the use of provisional ballots.
Congressional races: Each of Maryland's eight seats in the U.S. House of Representatives is up for grabs, though only the 1st District race - between Republican state Sen. Andy Harris and Democrat Frank Kratovil, the state's attorney for Queen Anne's County - is considered highly competitive.
The district, which includes the Eastern Shore as well as parts of Baltimore, Harford and Anne Arundel counties, has tended to vote Republican in statewide and national elections, but many observers now consider it a toss-up.
The contest has taken on many of the hard-knuckled themes in the presidential race. Harris has characterized his opponent as a tax-and-spend liberal whose ideas are outside the conservative mainstream. Kratovil has accused his rival of lying and has seized on the economy as a top issue.
Yesterday, the two candidates made morning television appearances before canvassing the district.
In the other races, an incumbent sweep is expected among Democrats including Rep. Elijah E. Cummings, who is heavily favored over Republican Michael Hargadon in the 7th district that includes parts of Baltimore City and Baltimore and Howard counties.