ST. LOUIS • Gov. Jay Nixon on Saturday vetoed a Republican-brokered proposal to reconfigure the state's Congressional districts, setting up a race against the clock as the legislative session winds to an end.

Politically, it's little surprise that Nixon, a Democrat, nixed a map that would have likely cost his party a seat in the U.S. House.

But if the governor and Republican leadership in the state Legislature don't agree on a map before lawmakers go home in two weeks, than drawing the new boundaries could fall to the courts.

In his veto letter, Nixon said he was rejecting the map because it "does not adequately protect the interests of all Missourians."

"I have taken this action expeditiously in order to provide the General Assembly the opportunity to pass legislation with appropriate Congressional district boundaries," Nixon wrote.

Because the U.S. Census showed Missouri growing at a slower rate than the rest of the nation, the state must shed a Congressional seat in 2012.

The process of drawing a new map that reflects eight districts instead of nine falls to the Missouri General Assembly, which is controlled by Republicans.

On Wednesday, the state House and Senate passed a map that axes the seat of U.S. Rep. Russ Carnahan, merging his district with the one currently held by another St. Louis Democrat, U.S. Rep. Lacy Clay.

In a statement Saturday, Carnahan applauded Nixon's veto, saying the rejected map would have "sliced and diced the St. Louis region."

The map would have given members of Congress from southeast and central Missouri a greater share of the St. Louis area, reapportioning to them parts of St. Charles and Jefferson County.

Nixon is from Jefferson County, and may be sensitive to a proposal that dilutes the area's influence.

That plan, however, has been scrapped, unless Republicans can engineer an override of Nixon's veto.

While Republicans in the Senate have the numbers to do so, the House stands 13 votes shy of pushing the previously approved map through over the governor's objection.

What happens next hinges on cooperation between Nixon and Republicans in the Legislature.

If no map is agreed upon by May 13, Nixon can reconvene lawmakers in a special session, though the governor's Saturday veto letter suggested he would like to see action on a new proposal this session.

Should legislators fail to forge a compromise -- or an override -- the courts would be next in line for the task.

State Rep. John Diehl, R-Town and Country, chairman of the House redistricting committee, said he would likely reach out to Nixon to gauge any specific objections to the GOP map.

Diehl said that garnering an override is not as daunting as the numbers would suggest. Legislators, he said, would be amenable to overruling the governor to avoid a handoff to the courts.

"You're also going for certainty," Diehl said, "instead of the uncertainty of what a map may bring if it goes to court."

Diehl's Senate counterpart, State Sen. Scott Rupp, R-Wentzville, predicted that the veto would not bring Republicans back to the drawing table.

"The map that we passed, I think, is a very good map," Rupp said. "I don't see any reason to go back and start over just because Gov. Nixon doesn't like it."