WASHINGTON (AP) — Barack Obama seized command of the race for the White House today night, defeating John McCain in Ohio and Iowa and building a near insurmountable Electoral College advantage in his historic bid to become the first black president.

Fellow Democrats gained strength in both houses of Congress.

Obama's Ohio victory denied McCain particularly precious territory. No Republican has ever won the presidency without the state.

The 47-year-old Illinois senator watched returns at a downtown Chicago hotel, then went home to a family dinner after a marathon campaign across 49 states and 21 months.

A jubilant crowd of thousands gathered in Grant Park across town on an unseasonably mild night. Cheers went up each time Obama was announced the winner in another state. The roar was particularly loud when Pennsylvania fell — the Democratic-leaning state where McCain had tried hardest to break through.

A survey of voters leaving polling places showed the economy was by far the top Election Day issue. Six in 10 voters said so, and none of the other top issues — energy, Iraq, terrorism and health care — was picked by more than one in 10.

Obama swept through traditionally Democratic states in the East and Midwest.

McCain countered in normally secure Republican territory.

That left a string of battleground states. All had voted for President Bush in his narrow victory in 2004, but Obama invested heavily in hopes of succeeding Bush as the nation's 44th president.

In addition to Ohio and Iowa, he led narrowly in Florida and by even less in Virginia and North Carolina.

Interviews with voters suggested that almost six in 10 women were backing Obama nationwide, and men leaned his way by a narrow margin. Just over half of whites supported McCain, giving him a slim advantage in a group that Bush carried overwhelmingly in 2004.

The results of The Associated Press survey were based on a preliminary partial sample of nearly 10,000 voters in Election Day polls and in telephone interviews over the past week for early voters.

Obama had 202 of the 270 electoral votes needed to win the White House. McCain had 80.

The Democrat's states included Iowa, Ohio, Wisconsin, Michigan, New York, Rhode Island, Minnesota, Pennsylvania, New Hampshire, Vermont, Connecticut, Delaware, Illinois, Maine, Massachusetts, Maryland and New Jersey, as well as the District of Columbia.

McCain had Utah, Arkansas, Kansas, Kentucky, Tennessee, Oklahoma, Wyoming, Alabama, South Carolina, Louisiana, West Virginia and North Dakota.

The nationwide popular vote was remarkably close. Totals from 27 percent of the nation's precincts showed Obama with 50.2 percent and McCain with 48.8.

Democrats celebrated Senate successes in Virginia, where former Gov. Mark Warner won an open seat, and in New Mexico, where Rep. Tom Udall did likewise. In New Hampshire, former Gov., Jeanne Shaheen defeated Republican Sen. John Sununu in a rematch of their 2002 race, and Sen. Elizabeth Dole fell to Democrat Kay Hagan in North Carolina.

That wasn't the end of the Democratic targets, though. Republicans all but conceded in advance they would lose a seat in Colorado, and perhaps elsewhere.

Democrats also looked for gains in the House. They found their first in Florida, defeating Rep. Tom Feeney, and another in Connecticut, where 22-year veteran Chris Shays was swept away by the Democratic tide.

The resurgent Democrats also elected a governor in one of the nation's traditional bellwether states when Missouri Attorney General Jay Nixon won his race.