C.A. Dutch Ruppersberger of Baltimore County and Christopher Van Hollen Jr. of Montgomery County won in contests that attracted the attention of both national parties.
Incumbents easily won re-election to the state's six other seats in the House of Representatives.
In the 2nd District, Ruppersberger, 56, the Baltimore County executive, defeated former Rep. Helen Delich Bentley, 78, reversing two decades of Republican victories in the mostly Democratic district centered on the county's east side.
Ruppersberger waded through a throng of supporters last night in a confetti-filled ballroom at the Towson Sheraton while the theme from Rocky played in the background.
"Helen was a great, great public servant," Ruppersberger said. "She was tenacious, and I think it's important that we acknowledge that she ran a great race. But we won the race."
Bentley, jabbing at Democrats to the last, conceded defeat about 11 p.m., saying that even in a losing effort, her campaign may have provided a boost to Republican Robert L. Ehrlich Jr. - who gave up the congressional seat to run for governor.
"It appears our efforts in Parris Glendening's new 2nd District have fallen short," she said to a cheering crowd at the American Legion post in Towson. "But we have provided a solid backbone for Ehrlich's campaign."
In suburban Washington's 8th District, Van Hollen, 43, a state senator, defeated Republican Rep. Constance A. Morella, 71, a popular eight-term incumbent.
"I am just so very fortunate," said Morella in conceding. "I've had the opportunity to move the issues that affect all of us. For all of this, I thank all of you. I will always remember all of you in my heart."
Van Hollen waited for Morella's concession, then entered the ballroom at a Silver Spring country club with his wife and two young children as a band played James Brown's "I Feel Good."
"This is not a vote against Connie Morella," he said. "It's a vote for change in the district and change in leadership."
The two Maryland districts were viewed by both national parties as swing seats in the battle for control of the House, where Republicans began the evening with a 223-208 advantage. The parties sent in money and political stars, including Bush and his wife, Laura, and New York Sen. Hillary Rodham Clinton, the former first lady.
The results allowed Maryland Democrats to break the 4-4 tie between the parties in the state's congressional delegation. The split is now 6-2.
The Democrats used redistricting, the remapping of congressional districts that follows every census, to improve the party's prospects in both districts by adding precincts with heavy concentrations of Democratic voters.
Ruppersberger is only the second Baltimore County executive to be elected to higher office; Spiro T. Agnew, who became governor and vice president, was the first.
When his plans for a gubernatorial bid faded last fall, Ruppersberger let it be known that he would be interested in running for Congress, provided that Governor Glendening could draw him a sufficiently Democratic district.
In the campaign, Bentley, who had held the seat for 10 years until giving it up to run for governor in 1994, emphasized her advocacy for the Port of Baltimore and her record of constituent service. She also stressed the Republican leadership's promise that her seniority and seat on the powerful House Appropriations Committee would be restored if she were elected.
But demographics of the district made the race difficult for Bentley; the new 2nd District is 68 percent Democratic.
In the 8th District, based largely in Montgomery County with a sliver of Prince George's, Morella was trying to duplicate a proven formula: Win the votes of a huge majority of Republicans, a smaller majority of independents and at least a quarter of the district's Democrats. Democrats enjoy a voter registration advantage in the district of nearly 2-to-1.
But this year, there was a difference in Morella's style. For the first time in her congressional career, she attacked her opponent by name in television ads. Among other accusations, she said that Van Hollen backed legislation to cut income taxes for Maryland's wealthiest citizens. She also alleged that he had distorted the record of Del. Mark Shriver, Van Hollen's opponent in the primary.
Van Hollen accused Morella of trying to smear his record in the state Senate. But he focused less on Morella than on urging the district's Democrats to do their part to help the party regain control of the House.
The 8th District hasn't been in Democratic hands since former Rep. Michael Barnes stepped down to run for the Senate in 1986.
Polling places were themselves a story. Montgomery County, which bogged down in posting returns during the primary as it adjusted to new touch-screen machines, was faster last night but suffered a few glitches.
In the 19th District, the word "Democratic" appeared mistakenly in screen instructions. Election workers scrambled to print a notice that the word should not have been there.
In other races, 6th District GOP Rep. Roscoe G. Bartlett won his sixth term by defeating congressional staff member Donald DeArmon for the second election in a row, and 1st District GOP Rep. Wayne T. Gilchrest gained a seventh term with an easy victory over activist Ann D. Tamlyn.
Democratic incumbents re-elected were 5th District Rep. Steny H. Hoyer, senior member of the delegation with 21 years' service, who beat business consultant Joseph T. Crawford; 7th District Rep. Elijah E. Cummings, who beat computer scientist Joseph E. Ward, a former Democrat; 3rd District Rep. Benjamin L. Cardin, who defeated lawyer Scott Conwell; and 4th District Rep. Albert R. Wynn, who beat behavioral researcher John B. Kimble. They will be in their fourth, ninth and fifth terms, respectively.
Sun staff writer David L. Greene and correspondents Liz Babiarz, Dave Pittman, Raymund Flandez and Hattie Brown contributed to this article.