WASHINGTON (Reuters) - What if it's a tie?
A handful of battleground states are likely to determine the November 4 U.S. presidential election and it's possible that Republican John McCain and Democrat Barack Obama could split them in a manner that leaves each just short of victory.
If that happens, the Democratic-controlled House of Representatives would pick the president but it's unclear whether Democrats would have enough votes to send Obama to the White House.
The House last decided an election in 1824. But the legal skirmishing and partisan rancor would probably resemble a more recent election -- the 2000 vote in which Republican George W. Bush narrowly defeated Democrat Al Gore after a disputed Florida vote count and legal battle.
"This would be the seamy side of democracy, the lobbying and the money would be so intense," said American University history professor Allan Lichtman.
In the United States, presidential elections are determined on a state-by-state basis rather than a nationwide popular vote. Each state, along with the District of Columbia, is allotted a number of votes in the Electoral College that correspond to the number of representatives it has in Congress. To become president, a candidate must win at least 270 electoral votes.
If McCain wins Virginia, New Hampshire, Florida and Ohio but loses Pennsylvania, Colorado, New Mexico and Iowa to Obama, both candidates could end up with 269 electoral votes.
Other, less likely scenarios -- McCain losing Virginia and New Hampshire but winning Michigan, for example -- also could result in a tie.
Under the U.S. Constitution, the House would then decide the election when it meets in January, with each state getting one vote -- regardless of its size -- if the chamber has to break a tie.
Democrats, who control the 435-seat House, outnumber Republicans in 27 state congressional delegations and could see that number rise in the November elections.
Republicans have a majority in 21 state delegations. Two states have an equal number of Republican and Democratic representatives.
Some members could feel pressure to vote for the other party's candidate if he carried their state or district or if he won a clear margin of the national popular vote, said Northwestern University law professor Robert Bennett.
They would also be under extraordinary pressure from party leaders to stick together.
"There would be bargaining in that context and lots of room for rancor and bitterness. It would be a mess," Bennett said.
The dispute probably would not be confined to Congress.
"Do you believe for one moment that this won't end up in the courts?" Lichtman said.
Other possible scenarios, according to Bennett:
* Before the House meets, the Obama and McCain campaigns could try to convince the Electoral College voters who actually cast each state's electoral votes to switch their support. This has happened occasionally in past elections but has never affected the outcome of an election. Electors in roughly half of the states are bound by law to honor the popular vote.
* While the House picks a president, the Senate picks the vice president in the event of a tie. The Democratic-controlled chamber could pick Democratic vice presidential candidate Joe Biden even if McCain wins the House vote.
* The newly minted vice president could become acting president if the House doesn't reach a resolution by the time President George W. Bush leaves the White House on January 20.
* House Speaker Nancy Pelosi would become acting president if neither chamber could settle on a president or vice president but she would have to resign her post.
Editing by David Alexander