The Republican presidential race is entering a crucial phase but the latest polls show there is no clear front-runner to unseat U.S. President Barack Obama in November.

Pennsylvania Senator Rick Santorum and former Massachusetts Governor Mitt Romney have emerged as the two favorites among Republican voters. And a nationwide poll released Wednesday by Quinnipiac University shows Santorum surging ahead, leading Romney by 9 percentage points.

But polls finds Santorum would lose to President Obama in the general election, while a Obama-Romney race would be too close to call.

Ahead of Wednesday night's nationally telvised debate in Arizona, Romney went on the attack, saying Santorum's voting record in Congress is not that of a fiscal conservative.

Romney's comments come as his campaign is paying millions of dollars for ads trying to paint Rick Santorum as a big spender.

Santorum says that is not true, claiming he took on the tough issues, including Medicare, Medicaid and social security.

Political analysts say Wednesday night's debate – which will also feature former House Speaker Newt Gingrich and Texas Congressman Ron Paul – could leave a strong impression on voters in Arizona and in Michigan, which hold primaries next week.

And two weeks from now is so-called “Super Tuesday,” when voters in 10 states head to the polls to choose a challenger to take on President Obama in the general election.