SPRINGFIELD, Ill. – The Senate on Tuesday approved an earlier presidential primary election in Illinois, a Democratic plan to help favorite son Barack Obama.

Legislation to make the primary Feb. 5, instead of March 20, passed the Senate 48-10. Gov. Rod Blagojevich has promised to sign it.

Supporters said the goal was not simply to aid Obama. They argued Illinois should play a bigger role in determining the presidential nominees.

“Illinois is one of the largest states, it’s the bellwether of the United States,” said Sen. Terry Link, D-Vernon Hills. “We should decide who the candidates are going to be in November.”

Obama, a U.S. senator and former member of the Illinois Senate, is a top contender for the Democratic nomination for president in 2008.

The state’s Democratic Party chairman, Illinois House Speaker Michael Madigan, introduced the idea of moving the primary election to give Obama an early victory in a big state. Often, nominees have been decided by the time of Illinois’ March primary.

Republicans complained that moving the date would increase the cost of campaigns and frustrate voters who already are tired of the long election process.

“They get tired of hearing the negative TV ads month after month after month after month. This will make those campaigns longer,” said Sen. Dale Righter, R-Mattoon.

Righter questioned whether the move actually would have much impact on Obama’s campaign or Illinois’ role in choosing the nominees because so many other states also are switching to early primaries.

A dozen states, including California and New York, already have moved their primaries to Feb. 5, and more are considering such a move. Florida lawmakers have voted to hold that state’s primary Jan. 29.