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ABC News' Michael Falcone reports:

The ink is not yet dry on Tuesday's Southern primaries, but the candidates are already gearing up for battle in two of the month's remaining contests: Illinois and Louisiana.

With recent polls showing Mitt Romney locked in a closer-than-expected race with Rick Santorum in Illinois,Romney's campaign is buying up air time ahead of the state's March 20 primary - to the tune of nearly $1 million.

The Romney campaign has reserved more than $800,000 worth of TV ad time on local broadcast channels, focusing on Chicago with smaller buys in the Springfield, Peoria and Rockford markets. The campaign is spending another $134,000 on cable ad purchases throughout the state, according to a Republican media buyer tracking the spending.

Romney is getting a big assist from the pro-Romney super PAC, Restore Our Future, which has already purchased more than $900,000 worth of airtime, according to Federal Election Commission filings. And sources tracking ad buys indicate the super PAC has bought up as much as $1.5 million more in TV time in just the last week. More than half of that is being spent in the greater Chicago area.

That means pro-Romney forces could wind up spending well over $3 million - and perhaps more - in Illinois.

A recent Chicago Tribune-WGN poll found Romney leading Santorum in the state, 35 percent to 31 percent.

Romney will be campaigning there before next Tuesday's primary. He is slated to attend a fundraiser in Peoria with Congressman Aaron Schock. And two Romney supporters - former U.S. House Speaker Dennis Hastert and State Treasurer Dan Rutherford, chairman of Romney's Illinois campaign - are doing a statewide fly-around on Wednesday.

Illinois is an expensive state for television advertising, and neither the Santorum campaign nor the pro-Santorum super PAC, have yet to make any ad buys there. Instead, Santorum's team has invested a modest amount - just over $30,000 - on the airwaves in Louisiana, which holds its primary on March 24.

The cable buy is about evenly split between New Orleans, Baton Rouge, Lafayette and Monroe, Louisiana.