The war of words in the Maryland race for the U.S. Senate grew more heated over the weekend, as three-term incumbent Sen. Barbara A. Mikulski (D) began airing a television ad challenging her opponent's charges that she favors tax increases and opposes military spending.

The ad criticizes Mikulski's GOP challenger, state Sen. Edward J. Pipkin, an Eastern Shore Republican, saying he is "slinging mud" and making "bogus charges." The 30-second spot cites a list of votes that the Mikulski campaign says show that Pipkin has distorted her record. The ad also accuses Pipkin, a former bond trader on Wall Street, of using "phony facts and made up numbers. . . . He's still dealing junk. . . . "

The new advertisement marks a shift in strategy for Mikulski, 68, who remains well ahead of Pipkin in recent polls in a state where registered Democrats outnumber Republicans by about 2 to 1. One poll last week showed Pipkin making some gains after he began airing his own television ads, which criticize Mikulski for her record on taxes, military spending and the environment. Pipkin has stepped up his public appearances in recent days.

Mikulski's campaign manager, Mike Morrill, said yesterday that Pipkin "is not interested in telling the truth, and we are calling him on it." The new Mikulski ad replaces a 30-second spot about her support for military veterans and veterans benefits, Morrill said. He said the campaign was also considering other ads about issues raised by Pipkin.

Pipkin, 47, who represents Queen Anne County, said yesterday that his ads were accurate.

"We are talking about her record, and what does she do? She attacks me personally," Pipkin said as he campaigned on Mikulski's home turf in Baltimore.

"I stand by every claim in every ad. We have documented every claim in every ad," he said.

Pipkin's ads say that Mikulski has voted for higher taxes 350 times in her Senate career, opposed new equipment for U.S. troops and military pay raises, and voted against funding for the B-2 bomber and the F-18 fighter. "Who knew?" the ads say. Pipkin's ads, which went on the air about two weeks ago, also introduce him and his family.

Morrill did not dispute all of the votes cited in Pipkin's ads but said that some came on bills Republicans introduced that packaged several issues. He said Mikulski has voted for military pay raises at least 17 times but on occasion opposed military bills for other reasons. Until now, Mikulski's ads have focused on her background, pointing to her working-class Baltimore roots and her votes on such issues as veterans benefits. The spots have not mentioned Pipkin, and Mikulski has only recently begun to mention him when she campaigns.

Mikulski's new ad began airing Saturday after Pipkin and Mikulski sparred late last week in a series of news releases and interviews about his portrayal of her voting record. Pipkin, who got into politics after leading a successful fight to prevent dredging and dumping of Chesapeake Bay materials on the Eastern Shore, said Mikulski had not worked hard to help block dumping and did not have a strong record on protecting the bay, an allegation her campaign disputes.

Earlier last week, the Mikulski campaign said that Pipkin violated federal campaign regulations, alleging that he did not notify her promptly when his campaign triggered the so-called millionaire amendment. The law, passed after the 2002 elections, raises contribution limits for any candidate running against a wealthy opponent who makes substantial personal contributions to his own campaign. Pipkin has contributed about $1.2 million to his campaign; Mikulski has collected about $5 million. Pipkin said his campaign has complied with the law.

Barbara Mikulski says her opponent's ads make "bogus charges" about her record. At right is Gov. Robert L. Ehrlich Jr. Edward Pipkin, who has been accused of violating federal campaign regulations, said he stands by every claim. A poll showed him making gains.