Two new public opinion polls give Democrat Barack Obama a sizable lead over Republican John McCain in the U.S. presidential race.  VOA National Correspondent Jim Malone has the latest on the election campaign from Washington.

One survey by the Los Angeles Times and Bloomberg News found Obama leading McCain by a margin of 49 to 37 percent.  Another poll earlier this week by Newsweek magazine put Obama's lead at 15 points.

Other recent surveys show McCain trailing by anywhere from three to six points.

Political experts say Obama's lead is likely due to increasing voter concerns about the weakening U.S. economy, especially the rising cost of fuel.

"High gas prices and job losses, the economic recession, but more generally, the economic insecurity associated with globalization, the stagnant wages of most ordinary American households," said Thomas Mann, a political scholar at the Brookings Institution in Washington. "I think all of that bodes well for Democrats in the campaign."

Given the Democrat's advantage on the economy, political strategists predict Senator McCain will focus on his experience in foreign policy and national security.

McCain sharply disagrees with Obama's plan to begin pulling U.S. troops out of Iraq shortly after taking office.

"I believe that we will withdraw over time," McCain said. "I believe that it will be set by facts on the ground, not by an artificial timetable.  And I believe we will come home with victory and honor, and not with defeat."

Public opinion polls have long showed most Americans do not believe the Iraq war was worth the cost.  But the polls also indicate they are divided over whether to withdraw U.S. troops before Iraq is stabilized.

Obama says he favors a measured approach to pulling U.S. troops out of Iraq.

"We have to be as careful getting out as we were careless getting in," he said. "I have proposed getting one to two brigades, combat brigades, out per month.  At that rate, we are talking about maybe 16 months to get our combat troops out."

On Friday, Senator Obama will make his first joint campaign appearance with former Democratic Party rival Hillary Clinton.  They will appear in the small town of Unity, New Hampshire, where the two candidates each received 107 votes in January's primary, in which Senator Clinton won the total state vote.

Clinton returned to work in the Senate this week for the first time since she suspended her presidential campaign and endorsed Obama earlier this month.