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.