About 25 percent of self-identified Republicans rated U.S. Sen. John McCain, R-Ariz., as most likable, followed by 23 percent who said Obama was most likable, a Washington Times poll indicated.

Obama and McCain are front-runners entering into Tuesday's primaries in Ohio, Texas, Rhode Island and Vermont. McCain could wrap up the GOP presidential nomination with victories in all four contests.

"There is something about Barack Obama that is hard to capture in polling and it's an enthusiasm, it's a freshness, it's an excitement he can generate that will certainly be a factor in the campaign," pollster Scott Rasmussen told the Times.

And among all adults surveyed, Obama, a U.S. senator from Illinois, was rated likable by more people than Sen. Hillary Clinton, D-N.Y., and McCain combined.

Concerning who'd be "toughest on matters of national security," McCain led with 39 percent to Obama's 17 percent and Clinton's 19 percent, the poll indicated.

Respondents also thought Obama smart, as 26 percent rated him the smartest among the candidates. Clinton earned 22 percent, McCain garnered 17 percent.

The poll of 1,000 adults was taken Feb. 26-27.