In the central part of the United States, presidential candidates from both parties are competing for delegates in states where polls show close contests. VOA's Greg Flakus has more on the story from Chicago.

In the central states there are only a few real battlegrounds, but the candidates are fighting hard for every delegate.

On the Democratic side, New York Senator Hillary Clinton has maintained a commanding lead in most states until recently. Polls taken after the January 26 South Carolina primary, which was won overwhelmingly by Illinois Senator Barack Obama, show him erasing much of Clinton's lead in many states.

Missouri could be a close call, even though the latest polls show Clinton well in the lead. Obama is now favored in Minnesota and is surging in smaller states like Kansas and North Dakota. Obama's mother was from Kansas and the state's popular two-term Democratic governor, Kathleen Sebellius has endorsed him.

The biggest prize in the heartland is Illinois, with its 185 delegates. Obama has a commanding lead in the state he represents in the Senate, although Clinton, who was born here, has pockets of strength in some Chicago suburbs.

In the Republican contest in Illinois, polls favor Senator John McCain, but former Massachusetts Governor Mitt Romney has made an all-out effort here, trying to rouse conservatives against McCain for his immigration reform bill and his opposition to tax cuts.

"Do we want to have a person lead our party and be our nominee who voted against the Bush tax cuts," asked Mitt Romney.

Romney is supported by former House Speaker Dennis Hastert, an Illinois congressman, who says McCain could never be counted on to support his party's policies in Congress.

But McCain has also been on the campaign trail here, defending his record, his conservatism and his loyalty to a Republican Party that he says has lost its way.

"We know why we lost the 2006 election, because we let spending get completely out of control," said John McCain. "Well, I am going to veto every pork barrel bill that comes across my desk."

Analysts say McCain could lock up his party's nomination with a big win on Super Tuesday and that Romney will need wins in at least a few major contests to remain viable.

The outcome of the primaries and caucuses held in the heartland may depend on rules established in each state and by each party as to how delegates are designated.

In Missouri's Republican race, for example, all 58 delegates go to the statewide winner. On the Democratic side, however, there are 88 delegates, 72 of which are allocated proportionally to candidates based on a formula that includes outcome in the state's nine congressional districts and the statewide vote. The state also sends 16 un-pledged delegates to the convention.

In both Tennessee and North Dakota, all Republican delegates are awarded to the candidate who can win two thirds of the vote, but are awarded proportionally if no candidate achieves that percentage. Colorado holds caucuses, but sends 46 un-pledged delegates to the Republican convention. Democrats in that state award 55 delegates based on proportion of the vote won by each candidate and also send 16 un-pledged delegates to their convention.