WASHINGTON — Barack Obama got no lasting boost from his ballyhooed trip last week to Europe and the Middle East, according to new national and swing state polls released Thursday.

And Republican John McCain may have benefited from his rival's visit to Iraq, Afghanistan and other countries, said Frank Newport, the Gallup Poll editor in chief.

"McCain voters may have been energized," Newport said. "They said they were paying more attention to the race."

Many experts caution, however, that polls in the summers of presidential election years seldom mean much, and they warn voters not to take them seriously.

"It's my strong personal opinion that nothing (in politics) between the primaries and the end of the political conventions means anything," said Brad Coker, the managing partner of Mason-Dixon Polling & Research.

Gallup's daily sampling of 2,682 registered voters found Obama with a 45-44 percent lead over McCain on Monday through Wednesday, a narrower margin that Obama had when he began his trip.

New Quinnipiac Polling Institute surveys Thursday found that Obama's lead in three key swing states has dropped in recent weeks. McCain spent last week in key states promoting his energy plan, particularly his proposal to lift the ban on offshore oil drilling.

That message may have resonated with voters, said Peter Brown, Quinnipiac assistant director.

"While Obama was on tour, trying to show voters he could handle world affairs, voters were home trying to fill their gas tanks," Brown said.

Obama was up 46-44 percent over McCain in Ohio and Florida, and ahead by 49-42 percent in Pennsylvania. The polls were conducted from July 23 through Tuesday.

No presidential candidate since 1960 has won the election without winning two of those three states, and Brown found that Florida and Ohio "are now too close to call."

He and others warned not to read too much into the state or national trends, as they cited three phenomena at work.

First, "It's summertime and nobody's paying much attention to politics," said Andrew Smith, the director of the University of New Hampshire Survey Center. His polls in that swing state show that McCain and Obama are close.

Smith said that Obama hadn't moved up because while his trip dominated political news coverage, no dynamic event such as a tight primary race or debates was stoking casual conversation.

Second, people are staying with their traditional political parties, as they often do in the summer before an election.

"It's almost like McCain and Obama are generic Republican and Democratic candidates," Newport said. "American presidential races are pretty well structured," he said, and even in November, most people tend to vote with the same parties they've backed for years.

Third, the Obama trip was a vivid reminder to Republicans that the Illinois senator is poised to run a strong, energetic campaign, so they'd better mobilize quickly.

Gallup's daily polls measure registered voters. But Gallup also reports on the mood of "likely" voters — generally those who are paying more attention to the race _and last Friday through Sunday, they gave McCain a 49-45 percent edge.

The latest Quinnipiac polls: http://www.quinnipiac.edu/x2882.xml?ReleaseID=1196

The daily Gallup polls:

http://www.gallup.com/poll/109177/Gallup-Daily-Obama-45-McCain-44.aspx