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 percent to 46 percent 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 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 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.

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 remain a vulnerability. In the poll, 63 percent say they are concerned he would pursue policies too similar to those of the current president..

In the new poll, taken Friday through yesterday, McCain leads Obama by 54 percent to 44 percent among those seen as most likely to vote. The survey of 1,022 adults, including 959 registered voters, has a margin of error of plus or minus 3 points for both samples.