U.S. Democratic presidential candidate Hillary Clinton questioned rival Barack Obama's experience in handling a national security crisis on Friday as polls showed her losing ground to Obama ahead of Tuesday's contests in Texas and Ohio.

The Clinton campaign released a new television ad for airing in Texas, which along with Ohio are crucial to her chances of reversing a string of losses to Obama. It shows children sleeping peacefully in bed as a narrator says:

It's 3 a.m. and your children are safe and asleep. But there's a phone in the White House and it's ringing. Something's happening in the world. Your vote will decide who answers that call.

The Clinton campaign hoped the new ad would convince voters she would be ready to act swiftly and decisively in case of another September 11-type crisis in the United States.

Clinton, a New York senator and former first lady once considered the favorite to win her party's presidential nomination, needs to win Texas and Ohio by wide margins next Tuesday or face the end of her candidacy.

Her struggling campaign got an important morale boost with the news that she had raised $35 million in campaign contributions in February, which was the most she had taken in in one month by far. Obama was expected to release figures soon showing he had out-raised her in February.

Obama struck back hard at Clinton over the ad in remarks to veterans at a town hall meeting at an American Legion post in Houston.

He said the ad raised a legitimate question, which he said had been answered by her 2002 Senate vote to authorize use of force in Iraq, which he said exposed poor judgment.

I will never see the threat of terrorism as a way to scare up votes, because it's a threat that should rally this country around our common enemies. That's the judgment we need at 3 a.m., he said.

OBAMA LEADS IN TEXAS; OHIO CLOSE

Clinton has repeatedly tried to question Obama's experience but the first-term Illinois senator, who would be the first black president, has ridden a wave of support with a call for sweeping change in Washington.

A Reuters/C-SPAN/Houston Chronicle poll released on Friday said Obama holds a slight lead in Texas, 48 percent to 42 percent, over Clinton, who would be the first woman president.

He trails Clinton 44 percent to 42 percent in Ohio -- well within the poll's margin of error of 3.8 percentage points. He had been losing to her in Ohio by double digits.

In the Republican race, front-runner John McCain holds commanding leads over his last major rival, former Arkansas Gov. Mike Huckabee. McCain, an Arizona senator, has built an unassailable advantage in delegates who will pick the nominee at the Republican Party convention in September.

The poll, conducted by Zogby International, found McCain with big double-digit margins over Huckabee in Texas and Ohio.

The Clinton campaign organized a conference call to say that anything but big victories by Obama in Texas, Ohio, Rhode Island and Vermont on Tuesday would be seen as a problem for him.

If, given the mantle of front-runner, with enormous financial resources given to them, they are unable to win these states, it sends a very clear signal that Democrats want this campaign to continue and there is some dissatisfaction with Sen. Obama's campaign, Clinton spokesman Howard Wolfson said.

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