Republicans thrived in Dallas' northern suburbs on Tuesday as they have in every recent election, winning judgeships, county races and seats in Congress by large margins.

But the lopsided results conceal what experts say was a major Democratic shift in suburbs both red and blue – even in bedrock conservative areas such as Allen, Denton and Plano.

In Collin and Denton counties, President-elect Barack Obama received 70,000 more votes than Sen. John Kerry did in 2004. Sen. John McCain, by contrast, collected 19,000 more votes than George W. Bush.

The numbers propelled some local races to their closest margins in years and Democratic vote totals to 2 ½ times what they were in 2000. Republicans also set voting records, though their gains were not as dramatic.

"The Democratic Party is motivated," said state Rep. Brian McCall, a longtime Plano Republican who won re-election Tuesday.

The suburban Democratic surge – fed by voter discontent over the economy, the current administration and other issues – played out to varying degrees nationally and helped carry Mr. Obama to victory in several battleground states.

The wave was far less noticeable in Republican bulwarks such as Texas, which voted for Mr. McCain. And experts and party officials agree that Democrats are at least several elections away from competing in suburban Austin, Dallas and Houston.

Still, Tuesday's surge fueled hidden Democratic gains. Experts likened the phenomenon here to a tsunami in the open ocean that is barely felt because it is far from shore.

The election also underscored the role of the suburbs as a political barometer for the nation and the frontier in the battle for the presidency.

"The last five presidential races have been decided in the suburbs," said Lawrence Levy, executive director of the National Center for Suburban Studies at Hofstra University.

Even in red-state Texas, the suburbs are at the center of what amounts to a political tug of war.

Urban centers such as Dallas have drifted Democratic in recent years. Rural communities such as Grayson and Wise counties, meanwhile, have grown more Republican.

In the middle are Collin and Denton counties, which in recent decades have witnessed explosive population growth and gradually are becoming more ethnically and politically diverse.

More than half of the nation's 300 million people now live in the suburbs. In Texas, an estimated 80 percent of the population lives in urban and suburban areas.

On Tuesday, many of those communities, even in staunch GOP states like Alabama, Idaho and Utah, turned more Democratic, statistics show. The same goes for Texas.

"There were huge Democratic gains in suburban Texas, but they barely register because Texas is so Republican," said Robert Lang, director of the Metropolitan Institute at Virginia Tech and a leading expert on suburban politics.

But, Dr. Lang added, "throw Collin County into the St. Louis suburbs and, all of a sudden, Missouri would be solidly blue and not red."

In some suburbs, including Montgomery County outside Houston and Comal County north of San Antonio, Democrats made little ground.

But heavy Latino and black turnout bolstered the party in several places where the GOP has traditionally dominated, such as Fort Bend County, southwest of Houston.

Despite the turnover, Republican candidates still won comfortably in Collin and Denton counties.

Mr. McCain collected just over 60 percent of the vote in the two counties combined. In both 2000 and 2004, Mr. Bush captured more than 70 percent of the vote.

Observers disagree over whether the wave represents a one-time boost or a lasting trend. Democratic officials hope they have set a foundation on which to build, while others believe the GOP's suburban dominance will continue.

"The time will come when Collin County is competitive, but it is still a GOP stronghold," said Michael P. McConachie, a political science professor at Collin College in Plano.

For Democrats in suburban Texas, the outlook may depend on the nation's mood when the next election arrives, Dr. Lang of Virginia Tech said.

"Suburbs are where the pain is felt the most: gas prices, home foreclosures," he said. "This is where the mood was very upbeat in 2004. The economy was strong and the suburbs were the beneficiaries. Then all the wheels came off."