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ABC News' Michael Falcone and Shushannah Walshe report:

In an attempt to blunt the effect of Mitt Romney advertising advantage in Michigan, a pro-Santorum super PAC announced on Thursday that it has purchased roughly $663,000 of television airtime in the state ahead of the Feb. 28 primary.

"As we've seen throughout this election cycle, the Romney campaign is good at two things: spending tons of cash and tearing others down.  It won't work here," said Stuart Roy, an adviser to the super PAC, the Red, White and Blue Fund. "While we won't get pulled into the type of 'spitting' match that Romney likes to engage in, we also won't let attacks go unanswered."

According to a media buying source the group booked the time on broadcast stations - most heavily in the Detroit area with smaller buys in places like Grand Rapids, Lansing and Traverse City.

The ads will begin running on Thursday.

Roy did not immediately say which ads his group planned to air, but noted that the buy will "match the Romney campaign and the Romney super PAC, Restore Our Future, advertising for the week leading into the Michigan primary."

But overall the Romney campaign and the pro-Romney super PAC has far outspent Santorum and his allies in Michigan. Restore Our Future began running ads in Michigan in late January and the group and the campaign have spent more than $1.6 million on the airwaves there.

The Santorum campaign reserved a modest amount airtime in Michigan - about $41,000 worth - and the Red, White and Blue Fund's efforts will help the former Pennsylvania senator narrow the spending gap.

The pro-Santorum PAC's largest donor, Foster Friess, said in an interview with ABC News earlier this week that he would continue to keep cash flowing to the group.

"If money is needed I want to be helpful," Friess said, but he declined to "say to what extent."

Recent polls in Michigan indicate that the race there is shaping up to be a two-person contest for first place between Romney, who was born there, and Santorum, who has been touting his blue-collar roots to voters.