WASHINGTON — Mitt Romney got a poll boost from his strong debate performance against President Barack Obama but it is too early to know how significant or lasting the bounce for the Republican challenger will be.

Gallup's September 30-October 6 poll of registered voters across the nation showed Obama had a five-point lead over Romney in the three days before last Wednesday's presidential debate.

But in the three days after the debate, that lead had melted away and the two candidates were tied at 47 percent apiece.

Obama still had a three-point edge, 49 to 46 percent, in Gallup's seven-day rolling average ending Saturday, which included polls before and after the debate.

"Even on this basis, the race has become somewhat more competitive compared with before the first debate," Gallup said. "Obama held four- to six-point leads in Gallup's seven-day tracking results in the eight days prior to the Oct 3 debate."

A separate national poll by the Pew Research Center conducted in the days after the debate showed Romney backed by 49 percent of likely voters and Obama with the support of 45 percent.

This represented a stunning reversal from a Pew poll conducted between September 12 and September 16 that gave Obama an eight-point lead among likely voters, but again it was unclear how quickly the Romney surge might evaporate.

The volatile national polls will only affect the result on November 6 if they translate to breakthroughs in key states like Virginia, Florida and Ohio, where Romney must win to have any chance of taking the White House.

Obama currently leads in nine of the 10 swing states.

The latest national polls are however an early measure of the damage done by Obama's lackluster performance against a more aggressive and energetic Romney in Denver.

Two more presidential debates await on October 16 and October 22. The vice presidential candidates, Democrat Joe Biden and Republican Paul Ryan, will go head-to-head in a one-off encounter on Thursday.