WASHINGTON  The Republican National Convention has given John McCain and his party a significant boost, a USA TODAY/Gallup Poll taken over the weekend shows, as running mate Sarah Palin helps close an "enthusiasm gap" that has dogged the GOP all year.

McCain leads Democrat Barack Obama by 50%-46% among registered voters, the Republican's biggest advantage since January and a turnaround from the USA TODAY poll taken just before the convention opened in St. Paul. Then, he lagged by 7 percentage points.

The convention bounce has helped not only McCain but also attitudes toward Republican congressional candidates and the GOP in general.

"The Republicans had a very successful convention and, at least initially, the selection of Sarah Palin has made a big difference," says political scientist Larry Sabato of the University of Virginia. "He's in a far better position than his people imagined he would be in at this point."

However, in an analysis of the impact of political conventions since 1960, Sabato concluded that post-convention polls signal the election's outcome only about half the time. "You could flip a coin and be about as predictive," he says. "It is really surprising how quickly convention memories fade."

McCain has narrowed Obama's wide advantage on handling the economy, by far the electorate's top issue. Before the GOP convention, Obama was favored by 19 points; now he's favored by 3.

The Republican's ties to President Bush remains a vulnerability. In the poll, 63% say they are concerned he would pursue policies too similar to those of the current president. Bush's approval rating is 33%.

In the new poll, taken Friday through Sunday, McCain leads Obama by 54%-44% among those seen as most likely to vote. The survey of 1,022 adults, including 959 registered voters, has a margin of error of +/— 3 points for both samples.

Among the findings:

• Before the convention, Republicans by 47%-39% were less enthusiastic than usual about voting. Now, they are more enthusiastic by 60%-24%, a sweeping change that narrows a key Democratic advantage. Democrats report being more enthusiastic by 67%-19%.

• Alaska Gov. Sarah Palin, a national unknown before McCain chose her for the ticket 10 days ago, draws a strong reaction from voters on both sides. Now, 29% say she makes them more likely to vote for McCain, 21% less likely.

Obama's choice of Delaware Sen. Joe Biden as running mate made 14% more likely to vote for the Democrat, 7% less likely.

• McCain's acceptance speech Thursday received lower ratings than the one Obama gave a week earlier: 15% called McCain's speech "excellent" compared with 35% for Obama.