WASHINGTON (Reuters) - U.S. President George W. Bush on Thursday sharply criticized foreign policies advocated by Democratic front-runner Barack Obama, saying it would be a mistake to meet the leaders of Iran and Cuba without preconditions or swiftly change course in Iraq.

“I’m not suggesting there’s never a time to talk, but I’m suggesting now is not the time ... to talk with Raul Castro,” Bush told a White House news conference after being asked about Obama’s willingness to meet with the new Cuban president, Raul Castro.

“It will send the wrong message. ... It will give great status to those who have suppressed human rights and human dignity,” Bush added, saying there was no difference between Raul Castro and his brother, Fidel, who recently stepped aside as president because of ill health.

It was the first major instance of Bush injecting himself into the presidential race to choose who will succeed him in the November election, with his unpopular Iraq war a major debating point on the campaign trail.

Asked about Obama’s remark during a recent debate with rival Hillary Clinton that he advocated withdrawing from Iraq but might send troops back to avoid al Qaeda forming a base there, Bush said U.S. forces had been fighting in Iraq for four years to prevent that from happening.

“I believe Senator Obama better stay focused on his campaign with Senator Clinton, neither of whom has secured their party’s ... nomination yet,” Bush added.

Obama quickly fired back, saying: “The American people aren’t looking for more of a do-nothing Cuba policy that has failed to secure the release of dissidents, failed to bring democracy to the island and failed to advance freedom for 50 years.”

Obama repeatedly has advocated meeting without preconditions with leaders of such hostile nations as Cuba and Iran, saying current U.S. policy is not working and it is time for a fresh look at ways to improve relations.

“The next president has a job to do to repair our image and to send a signal ... that a new era is being ushered in and that we are not afraid to talk to anybody, including those who we have grave problems with,” Obama said.

MCCAIN, OBAMA TRADE BARBS

Bush’s comments on Obama’s policies reflected how closely he is watching the campaign and how eager he is to guard his legacy. He has yet to formally endorse the Republican front-runner, Arizona Sen. John McCain, but is expected to do so.

McCain, a strong Iraq war supporter and former prisoner of war in Vietnam, continued his attacks on Obama on Thursday, criticizing the Illinois senator for pledging to withdraw from Iraq.

“The decision to unilaterally withdraw from Iraq and set a date for withdrawal would lead to chaos,” McCain told reporters at a Houston airport. “Al Qaeda will announce to the world that they have defeated the United States of America.”

Slideshow ( 6 images )

Obama fended off the criticism.

“The American people aren’t looking for tough talk about fighting for 100 years in Iraq, because they know we need to end this war, finish the job in Afghanistan, and take the fight to al Qaeda,” he said.

Obama’s rejection of what he calls conventional thinking in Washington has put him in the driver’s seat to seize the Democratic nomination from Clinton, long considered the inevitable nominee.

Slideshow ( 6 images )

The exchange came as a new Pew Research Center poll showed Obama with a broad-based advantage over Clinton before critical March 4 contests in Texas and Ohio to select a Democratic presidential candidate for the November election.

The poll found Obama leading Clinton 49 percent to 40 percent among Democratic primary voters. But 70 percent of Democratic voters now see Obama as the likely nominee, including more than half of Clinton supporters, the poll found.

Clinton, who has strong support among low-income voters, toured the economically struggling Appalachian foothills of southern Ohio on Thursday to tout her proposals to help lower-income and middle-income families.

The former first lady and New York senator announced she had raised $35 million in the past month, but Obama reportedly was poised to surpass her in fundraising again.

Obama has consistently led Clinton in fundraising, an advantage that showed in advertising figures for Texas and Ohio. Media research firm Nielsen reported on Thursday that Obama aired 80 percent more ads in Ohio than Clinton between February 1 and February 24, and nearly 50 percent more in Texas.

(Additional reporting by Jeff Mason, Andy Sullivan and John Whitesides; editing by David Wiessler and Eric Beech)