President Bush and Senator John Kerry are locked in a tense battle for crucial electoral votes that will determine which of them will be in the White House. As counting continues, all eyes are on three key states, which could determine the result of the election.

The number of states favoring Republican candidate George W. Bush steadily increased through the night, with the president maintaining the lead in electoral votes.

U.S. television networks were cautious in their projections, particularly on states crucial to victory for either Mr. Kerry or President Bush. But all eyes are focused on Florida, Ohio and Pennsylvania. These three states comprise one-quarter of the 270 electoral votes (out of 538 total) either candidate would need to win the presidency.

In his biggest victory so far, Mr. Kerry won the state of Pennsylvania with 21 electoral votes, where he and Mr. Bush made numerous visits during their campaign for the White House.

Florida, where there was so much controversy in the 2000 election, has 27 electoral votes.

John Kerry and wife, Teresa Heinz Kerry

Kerry spokesman Joe Lockhart told reporters Senator Kerry remains optimistic about Florida, as well as Ohio, pointing to votes yet to be counted from heavily Democratic areas in both states.

Turnout could be the highest in more than four decades, and significantly more than the 2000 election. The delayed and controversial conclusion of that vote formed the basis of political divisions forming the backdrop of the 2004 vote.

Watching the results in Washington, Mr. Bush told reporters he remains confident of victory.

Senator Kerry, the Democratic candidate, said earlier in Boston he is confident he successfully made the case to the American people on the need for change.

Although voting went smoothly for the most part, organizations monitoring the polls said there were scattered problems in some states.

And there was new controversy over reports quoting Florida election officials that tens of thousands of absentee ballots might not be counted until Thursday.

The independent presidential candidate in the election, Ralph Nader, drew far fewer votes than he did in 2000, when many Democrats blamed him for drawing support away from former Vice President Al Gore, who lost to President Bush in electoral votes.