Washington ? As a rule, a new president’s choice of a secretary of transportation makes few headlines, even when the appointee is a member of the opposition. In 2001, George W. Bush decided to name as transportation secretary Norman Mineta, a former congressman from California, to be the token Democrat in his Cabinet, and no one noticed. And no one except for Mark Shields, who lavishly praised the appointment, paid much attention last week when Barack Obama made Ray LaHood, the retiring representative from Peoria, Ill., the second Republican in his Cabinet.

This one, however, is loaded with meaning because LaHood is no ordinary congressman. He has been, as Shields pointed out, one of the most widely respected members of the House, a leader in the uphill struggle for comity between the parties, a throwback to the days of his old boss Bob Michel, the minority leader who resisted Newt Gingrich’s scorched-earth tactics. Such was LaHood’s reputation for fairness that he was the natural choice to preside over the House during the explosive impeachment proceedings against Bill Clinton.

The significance of his accepting Obama’s offer goes beyond the signal it sends of the new president’s seriousness about outreach to moderate Republicans. As transportation secretary, LaHood will be at the center of the road and bridge construction projects Obama plans to make the highlight of his almost trillion-dollar stimulus program.

All the signs are that the stimulus spending will be opposed by congressional Republicans, whose shrunken ranks are increasingly dominated by right-wing Southerners who care not what their stance does to harm the party’s national image.

The spectacle of LaHood facing off in congressional testimony against those naysayers will dramatize a split that is crippling the GOP.

The danger became apparent as far back as 2007. With Bush weakened by the Iraq War, Hurricane Katrina and the midterm election losses of 2006, a Southern-led revolt killed his immigration reform bill. Junior senators such as Jim DeMint of South Carolina directed the rebellion, and Minority Leader Mitch McConnell, unable to stem the insurgency, joined it.

The price was paid in the 2008 presidential campaign. Despite his personal credentials as a sponsor of comprehensive immigration reform, John McCain was caught in the backlash of anti-GOP voting by Hispanics. It contributed to his loss of Colorado, New Mexico, Nevada, Florida and other states.

The same thing happened this year when Bush supported a bailout for the Big Three auto companies. Led by Republican senators from Southern states where there are many foreign-owned auto plants, the Senate refused to cut off a filibuster against the bill providing bridge loans to General Motors and Chrysler. This time, the opposition was led by Bob Corker of Tennessee and Richard Shelby of Alabama. When the Senate failed by eight votes to cut off debate, Southern and border-state Republicans voted 16-2 against the measure. On a similar vote on the 2007 immigration bill, the Southerners split 17-3 against.

Even though Bush later used his authority to provide the loan, the defeat of this legislation at Republican hands will not be forgotten when GOP senators run for re-election in 2010 in states such as Ohio and Pennsylvania. It will also echo in industrial states such as Michigan, Indiana, Wisconsin, Illinois, California, New York and New Jersey, when Republicans try to challenge for Senate and House seats.

The Southern domination of the congressional Republican Party has become more complete with each and every election. This year, Republicans suffered a net loss of two Senate and three House seats in the South, but they lost five Senate seats and 18 House seats in other sections. No Republican House members are left in New England and they have become ever scarcer in New York, Pennsylvania and across the Midwest.

LaHood, who witnessed but did not welcome the Gingrich “revolution” in the House, has watched with growing alarm the decimation of the GOP in Illinois and surrounding states. As point man for Obama’s stimulus spending, he now poses the dilemma for his own party in the sharpest possible terms: Will congressional Republicans again sacrifice their political interest in order to satisfy their Southern-baked ideological imperatives?