WASHINGTON (AP) – Arizona Sen. John McCain challenged his remaining rivals for control of the Republican presidential race Tuesday in primaries and caucuses from Connecticut to California. Hillary Rodham Clinton and Barack Obama vied for Democratic delegates in a grueling campaign with no end in sight.

After an early series of low-delegate, single-state contests, Super Tuesday was anything but – primaries and caucuses spread across nearly half the country in the most wide-open presidential campaign in memory.

Clinton was winning only a slight edge among women and white voters, both groups that she has won handily in earlier contests, according to preliminary results from interviews with voters in 16 states leaving polling places. Obama was collecting the overwhelming majority of votes cast by blacks, and Clinton was gaining the votes of roughly six in 10 Hispanics.

In the GOP race, McCain had a small edge among voters calling themselves Republicans, a group he had not won in any of the earlier races. As usual, he was running strongly among independents. Former Massachusetts Gov. Mitt Romney was getting the votes of about four in 10 people who described themselves as conservative. McCain was wining about one-third of that group, and former Arkansas Gov. Mike Huckabee about one in five.

Democrats and Republicans alike said the economy was their most important issue. Democrats said the war in Iraq ranked second and health care third. Republican primary voters said immigration was second most important after the economy, followed by immigration and the war in Iraq.

The survey was conducted in 16 states by Edison Media Research and Mitofsky International for The Associated Press and television networks.

McCain was the Republican front-runner, all but unchallenged in winner-take-all primaries in New York, New Jersey and Connecticut. He looked for a home-state win in Arizona, as well.

Former Massachusetts Gov. Mitt Romney, struggling to sustain his candidacy, concentrated on Missouri and California as well as several caucus states.

Former Arkansas Gov. Mike Huckabee concentrated on a swath of Southern and border states. Texas Rep. Ron Paul had the fourth spot on the ballot.

In the first contest decided Tuesday, Huckabee won all 18 delegates at the West Virginia GOP convention after McCain’s supporters sided with him in a successful attempt to deprive Romney of a victory.

Democrats Obama and Clinton conceded in advance that neither was likely to emerge from the busiest day in primary history with anything more than a relatively narrow edge in convention delegates.

“Senator Clinton, I think, has to be the prohibitive favorite going in given her name recognition, but we’ve been steadily chipping away,” said Obama, seeking to downplay expectations.

As she voted in Chappaqua, N.Y., Clinton said, “The stakes are huge.”

Her aides conceded in advance that Obama might win more Super Tuesday delegates than the former first lady.

Already, both campaigns were looking ahead to Feb. 9 contests in Louisiana, Nebraska and Washington state and Feb. 12 primaries in Maryland, Virginia and the District of Columbia. And increasingly, it looked like the Democrats’ historic race between a woman and a black man would go into early spring, possibly longer.

Democrats had 1,681 Super Tuesday delegates to allocate in primaries in 15 states and caucuses in seven more plus American Samoa.

Clinton led Obama in the delegate chase as the polls opened, 261 to 202, on the strength of so-called superdelegates. They are members of Congress and other party leaders, not chosen by primary voters or caucus-goers. It takes 2,025 delegates to win the Democratic nomination.

Republicans had 1,023 delegates at stake in 15 primaries, six caucuses and one state convention.

The evening began with McCain holding 102 delegates, to 93 for Romney, 43 for Huckabee and four for Paul. It takes 1,191 to win the Republican nomination.

The de facto national primary was the culmination of a relentless campaign that moved into overdrive during Christmas week.

After a brief rest for the holiday, the candidates flew back to Iowa on Dec. 26 for a final stretch of campaigning before the state’s caucuses offered the first test of the election year. New Hampshire’s traditional first-in-the-nation primary followed a few days later, then a seemingly endless series of campaign days interspersed by debates and a handful of primaries and caucuses.

Along the way, the poorest performers dropped out: Democratic Sens. Joe Biden and Chris Dodd, New Mexico Gov. Bill Richardson and Rep. Dennis Kucinich of Ohio; and Republican Reps. Duncan Hunter and Tom Tancredo, and former Tennessee Sen. Fred Thompson.

Former Sen. John Edwards pulled out of the Democratic race last week, and former New York Mayor Rudy Giuliani left the Republican field.

Edwards offered no endorsement as he exited, instead leaving Obama and Clinton to vie for help from his fundraisers and supporters.

But Obama benefited from an endorsement by Sen. Edward M. Kennedy, who made a series of campaign appearances in California as well as his home state of Massachusetts.

Giuliani quit the race and backed McCain in the same breath, clearing the way for the Westerner in New York and New Jersey.

Giuliani’s departure also made it possible for California Gov. Arnold Schwarzenegger to back McCain. Schwarzenegger said he would not have done so as long as the former mayor was in the race.

Obama and Clinton spent an estimated $20 million combined to advertise on television in the Feb 5 states.

Obama spent $11 million, running ads in 18 of the 22 states with Democratic contests. Clinton ran ads in 17, for a total of $9 million.

Neither advertised in Illinois, Obama’s home state.