National polls show John McCain and Barack Obama on nearly even footing as they prepare to announce their running mates and attend their respective conventions in the next two weeks.

The tightening race suggests McCain's heightened attacks and steady succession of campaign ads have poked holes in Obama's image. The overseas conflict between Russia and Georgia also may have served to highlight McCain's foreign policy credentials.

Surveys consistently show McCain holding Obama to a narrow lead since Obama returned from his high-profile trip abroad last month.

McCain has been unable to seize the lead from his Democratic rival, but his performance in the surveys challenges the assumption that President Bush's low approval ratings make Obama the odds-on favorite in November.

The Gallup daily tracking poll -- which averages the last three days of polling on a rolling basis -- has shown an increasingly competitive race over the past five days.

Obama led McCain on Tuesday by just 1 percentage point, 45 to 44 percent. The survey of 2,648 registered voters had a margin of error of 2 points.

The Gallup poll has had the rivals tied two times since Friday, and since Thursday, Obama's lead has not stretched beyond 3 points.

A Los Angeles Times/Bloomberg poll released Tuesday showed Obama leading McCain by 45 to 43 percent, which would be within the poll's 3-percentage-point margin of error. The 2-point lead for Obama is down from 12 points in a similar survey in June.

Obama's favorable rating also went from 59 percent in the last poll to 48 percent in the latest survey.

Another national tracking poll from Rasmussen Reports on Tuesday showed Obama leading McCain by 3 percentage points, 45 to 42 percent. The three-day sampling of 3,000 likely voters had a margin of error of 2 points.

Obama enjoyed a 5-point lead in a national Quinnipiac University poll released Tuesday. However, that's down from the 9-point lead he enjoyed in a similar poll July 15.

The balance of the race, though, easily could tilt after the candidates announce their running mates and attend their conventions, which are rife with opportunities to both wow and disappoint the American electorate.

Both candidates are keeping their vice presidential choices close to the vest.

Speculation swirled Tuesday that Obama would announce his selection late in the week, before the first day of the convention in Denver, Colo., Monday. The candidate seemed to give a clue on the timing of the decision when he announced he would appear Saturday in Springfield, Ill., the city where he launched his campaign. The Obama campaign confirmed he would be appearing with his running mate, but it was not clear whether Obama would announce his vice presidential pick before that.

Meanwhile, McCain is expected to announce his vice presidential pick on Aug. 29, his 72nd birthday, in Dayton, Ohio, FOX News has learned.

In another good sign for McCain, the Gallup poll found that registered voters who have served in the military back McCain over Obama by 56 to 34 percent.

But McCain will have a tough road ahead if he hopes to strip himself of the underdog image.

Sources tell FOX News the Obama campaign plans to go after McCain hard at the Denver convention, escalating their effort to link him with Bush.

"They do not feel like they're slipping (in the polls), but they just think they need a clear definition of McCain supporting Bush economic policies, as well as being totally a D.C. figure," said one Democrat familiar with the Obama campaign's thinking.

Democratic strategist Mary Anne Marsh said Obama's got to get aggressive, because "if you don't fight back voters think you won't fight for them."

Obama has escalated his rhetoric in recent days.

"I don't intend to lose this election. John McCain doesn't know what he's up against right now," he said Tuesday evening at a town hall meeting in Raleigh, N.C.

McCain may still be quite vulnerable when it comes to his association with Bush. The Los Angeles Times/Bloomberg poll showed that 75 percent of voters believe the country is seriously on the wrong track.

And his favorable ratings in that poll were not stellar either. Forty-six percent of voters had a positive feeling about him in that survey; 38 percent had negative feelings about him.

FOX News' Major Garrett contributed to this report.