The call was based on an analysis of voter interviews, conducted for The AP by Edison Media Research and Mitofsky International.
Connecticut voters were also choosing five members of the U.S. House, voting on members of the state General Assembly and considering two ballot questions.
State election officials predicted a record turnout as high as 90 percent.
Secretary of the State Susan Bysiewicz said voting was heavy and steady across the state and many cities and towns, including New Haven, reported 30 percent voter turnout as early as 10 a.m. Many polling places had lines stretching outside and waits of 40 minutes or longer.
By 3:30 p.m., many towns in Connecticut reported 50 percent of registered voters already cast their ballots, even before the late afternoon rush. In Darien, voter turnout was estimated at 78 percent by 3:30 p.m.; 66 percent in Old Saybrook; 63 percent in Suffield; and 60 percent in Canton and Granby.
"The 2008 election will be one for the record books," Bysiewicz said. "All over the state, registrars and our teams on the ground are saying they have never seen this kind of turnout - ever."
Turnout was extremely heavy in cities like Bridgeport, Hartford and New Haven. Bysiewicz said some polling places saw double their normal volume of voters on Election Day Some 300,000 new voters have registered since the first of the year, pushing voter registration to its highest level in Connecticut history at nearly 2.1 million.
Bysiewicz said there were some minor problems with the state's optical scan voting machines. One machine in New Haven, for example, malfunctioned and was replaced with a backup machine, she said. Simsbury and Bristol each had a machine that had memory card malfunctions, and backup memory cards were used, she said.
Election officials said all ballots that were scanned by machines that malfunctioned would be scanned in other machines to make sure everyone's vote was counted.
"Turnout across the state has been very strong so far," Bysiewicz said in the early afternoon. "It is possible that by the close of the polls record numbers of Connecticut residents will have cast ballots in this historic election."
Polls opened at 6 a.m. and closed at 8 p.m., although state law allowed anyone in line at 8 p.m. be allowed to cast ballots.
In the 2004 presidential election, nearly 79 percent of eligible voters in Connecticut went to the polls.
In Congressional races, U.S. Rep. John Larson, D-1st District, defeated West Hartford Republican Joseph Visconti, and Rep. Rosa DeLauro, D-3rd District, won her 10th term by beating Republican Bo ItsHaky of Bethany.
The campaign in the 4th Congressional District, where recent polls show incumbent Republican Christopher Shays in a close race with Democrat Jim Himes, drew national attention.
Shays was seeking his 11th full term and was the only New England Republican in the House to withstand the Democrat sweep of 2006. Himes is a Greenwich businessman and member of the Greenwich town finance board.
In General Assembly races, Democrats were hoping to win enough seats to have a veto-proof majority in both the House and Senate.
Democrats hold a 107-44 advantage in the House, enough to override any vetoes by Republican Gov. M. Jodi Rell, but are one vote shy of the two-thirds majority in the Senate with a 23-13 advantage.
There were two statewide ballot questions. Voters were being asked if people whose 18th birthday falls between primary and general elections should be allowed to vote in the primary, and if the state should hold a convention to consider changes to the state constitution.
