WASHINGTON (Reuters) - Democratic presidential candidate Sen. Barack Obama said on Wednesday the United States must be willing to strike al Qaeda targets inside Pakistan, adopting a tough tone after a chief rival accused him of naivete in foreign policy.

Obama's stance comes amid debate in Washington over what to do about a resurgent al Qaeda and Taliban in areas of northwest Pakistan that President Pervez Musharraf has been unable to control, and concerns that new recruits are being trained there for a September 11-style attack against the United States.

Obama said if elected in November 2008 he would be willing to attack inside Pakistan with or without approval from the Pakistani government, a move that would likely cause anxiety in the already troubled region.

"If we have actionable intelligence about high-value terrorist targets and President Musharraf won't act, we will," Obama said.

The Illinois Democrat is trying to convince Americans he has the foreign policy heft to be president after a rival candidate, New York Democratic Sen. Hillary Clinton, questioned his readiness to be commander in chief.

Clinton last week labeled Obama naive for saying he would be willing to meet the leaders of Iran, Cuba, Syria, North Korea and Venezuela without preconditions in his first year in office.

A poll by The Wall Street Journal and NBC News said Clinton has widened her lead over Obama, going up to 43 percent in July from 39 percent in June. Obama tallied 22 percent, down from 25 percent in June.

Those polled cited Clinton's experience and competence highest among her positive attributes.

Obama said he would make hundreds of millions of dollars in U.S. military aid to Pakistan conditional on Pakistan making substantial progress in closing down training camps, evicting foreign fighters and preventing the Taliban from using Pakistan as a staging area for attacks on Afghanistan.

White House spokesman Tony Snow said Pakistan was working hard to fight al Qaeda and the Taliban, and Washington was doing what it could in support.

"At the same time, we recognize the sovereignty of the Pakistani government and realize that they're putting on a serious push ... They're taking the fight to al Qaeda," Snow said.

IRAQ AND AFGHANISTAN

Clinton, in an interview with the American Urban Radio Network, stressed the importance of the Pakistanis "taking the actions that only they can take within their own country."

But she did not rule out U.S. attacks inside Pakistan, citing the missile attacks her husband, then-President Bill Clinton, ordered against Osama bin Laden in Afghanistan in 1998.

"If we had actionable intelligence that Osama bin Laden or other high-value targets were in Pakistan I would ensure that they were targeted and killed or captured," she said.

Another Democratic candidate, former North Carolina Sen. John Edwards, said he would not hesitate to use force against extremists but said, "I believe we must first use maximum diplomatic and economic pressure on states like Pakistan and Saudi Arabia to take all necessary actions to stop al Qaeda."

Obama criticized President George W. Bush's emphasis on al Qaeda in Iraq and said as president he would end the war there and refocus efforts on the al Qaeda threat in Afghanistan and Pakistan by sending at least two additional U.S. brigades to Afghanistan.

He said that "because of a war in Iraq that should never have been authorized and should never have been waged, we are now less safe than we were before 9/11."

(Additional reporting by Missy Ryan)