C.A. Dutch Ruppersberger defeated Republican Helen Delich Bentley in Maryland's 2nd Congressional District last night, winning one of the most competitive House races and claiming a seat that Democrats have been trying to capture for almost 20 years.

Ruppersberger, the Baltimore County executive and a new darling of the Democratic Party, won by a decisive margin, overcoming a late surge in the campaign by Bentley, the fiery former congresswoman who had the support of some of the GOP's most popular personalities.

Like Maryland's 8th District race, the 2nd District, located largely in the Baltimore suburbs, drew national attention, attracted two high-profile candidates and became a top priority for both parties.

"It was a hard-fought race," Ruppersberger said last night, while supporters cheered around him. "I think my opponent did an excellent job. She had an excellent career. But I think this was about the issues, and my experience as county executive helped me."

Ruppersberger will replace Robert L. Ehrlich Jr., who decided not to seek reelection and run for governor. He helped persuade Bentley to enter the race.

Bentley spokesman Michael Kosmas said Bentley's campaign helped Ehrlich win the governor's race.

"We gave Bobby Ehrlich the backbone he needed," Kosmas said. "Bobby could go run for governor with a clean conscience because he knew there was a strong candidate standing behind him. We're proud of the role we played in that even if Helen didn't make it over the top."

Ruppersberger's victory, combined with that of Christopher Van Hollen Jr.'s 8th District win over incumbent Republican Constance A. Morella, also helped tip the balance of Maryland's congressional delegation, giving the Democrats a 6-2 edge. It had been evenly split.

In the state's other congressional races, incumbents were dominant. Republican incumbent Wayne T. Gilchrest handily defeated Democrat Ann D. Tamlyn by a margin of more than 3 to 1 in the 1st District, which covers parts of Anne Arundel and Baltimore counties and the entire Eastern Shore.

In the 3rd District, which includes parts of Baltimore and Anne Arundel, Baltimore and Howard counties, Benjamin L. Cardin, the Democratic incumbent, beat Republican Scott Conwell almost 2 to 1.

Rep. Albert R. Wynn (D) breezed by Republican John B. Kimble in the 4th District, which includes Prince George's County and eastern Montgomery County.

In the 5th District, which includes parts of Prince George's and Anne Arundel counties and all of Southern Maryland, 10-term Democratic Rep. Steny H. Hoyer trounced Republican Joseph T. Crawford.

Republican Rep. Roscoe G. Bartlett, seeking his sixth term representing Western Maryland's 6th District, defeated Democrat Donald M. DeArmon, who was running for a third time.

And in the 7th District, which includes most of Howard County, western Baltimore County and parts of Baltimore, three-term incumbent Rep. Elijah E. Cummings (D) won, defeating Republican Joseph E. Ward by a margin of almost 3 to 1.

Like Maryland's 8th District race, in which Van Hollen unseated Morella, the 2nd District attracted national attention and became a top priority for both parties.

The 2nd District curves around most of the Baltimore Beltway, including slices of Baltimore and Anne Arundel, Baltimore and Harford counties.

After Ehrlich announced that he would not seek reelection but run instead for governor, Democrats thought they would have their best chance of winning the district in years. Needing to pick up just six additional seats to win control of the House, the national party threw its weight -- and money -- behind Ruppersberger, a gregarious politician who won every precinct in his last bid for county executive.

After some infighting, the GOP countered with Bentley, a tough, political veteran who had represented the district from 1985 to 1994.

But the district isn't the same as the one she once represented. During the once-a-decade redistricting, Gov. Parris N. Glendening (D) drew the boundary lines to favor Ruppersberger, 56, who faced term limits and could not run for county executive again. He had been thinking of running for governor but decided to run for Congress when the national party said it would help him win the seat.

During the campaign, Ruppersberger called for an affordable prescription drug program for seniors and vowed to protect Social Security.

He raised more than $1 million as of last month and was feted by top party leaders such as House Minority Leader Richard A. Gephardt (D-Mo.) and the minority whip, Nancy Pelosi (D-Calif.). Several House members have taken Ruppersberger under their wing, helping him understand the nuances of Congress. And the popular Baltimore mayor, Martin O'Malley, appeared in ads with him.

"The party has been great. They have been with us just about the entire time financially and with advice," said Binetti, Ruppersberger's spokesman. "They've really helped Dutch focus his abilities on what it takes to win a congressional race."

During her campaign, Bentley, 78, has also gotten high-profile support -- but a lot of that didn't come until the final weeks of the campaign.

"Our party, I think, was a little bit behind the curve," said Kosmas, Bentley's spokesman. "They did not jump in with the big money until later."

Democrat C.A. Dutch Ruppersberger celebrates in a shower of confetti his victory over Helen Delich Bentley in the suburban Baltimore district.