In an unusual move, the top Republican in the U.S. Senate is campaigning to unseat the chamber's top Democrat.

The U.S. Congress is in recess this week, and many lawmakers are campaigning for reelection or seeking to boost the electoral prospects of their fellow Democrats or Republicans.

One-third of the Senate and all of the House seats will be up for grabs in November elections.

Much attention is being focused on contests in the Senate, where Republicans hold a slim majority, 51 of the 100 seats.

The top Republican in the Senate, Majority Leader Bill Frist of Tennessee, wants to increase the number of Republicans in the chamber to better promote President Bush's policies. He accuses Democrats, led by Senate Minority Leader Tom Daschle of South Dakota, of using parliamentary tactics to block Mr. Bush's legislative priorities from becoming law.

So in a break with tradition, Mr. Frist is campaigning against his Democratic counterpart. In recent days, he has attended fundraisers and campaign appearances in South Dakota for a former Republican congressman, John Thune, who is seeking to unseat three-term Senator Daschle in a tight race.

The Senate historian's office cannot recall another time, at least in the past half century, when one Senate leader went to the home state of another to campaign against him.

Some Democrats, including Senator Robert Byrd of West Virginia, consider Mr. Frist's activities a breach of Senate protocol, where cooperation is considered essential. ?What has become of civility, old-fashioned civility? What has become of comity? What has become of comity in this branch he asked. ?It used to be unheard of for Senate leaders to seek an active role against each other in campaigns. That time has apparently gone. Gone! Has honor gone too? Who cares about honor when a Senate seat might be gained

Senator Frist defended his efforts on behalf of Mr. Thune and noted he is campaigning in support of a number of Republican Senate candidates. ?As majority leader of the United States Senate, I am elected to be the leader of the Republican Party in the United States Senate,? he said. ?It is a little bit disingenuous to say that as leader of the Republican Party in the United States Senate in a closely divided Senate and in close races that you are not going to participate in some shape or form in those races.?

In an interview with radio reporters, Senator Frist noted that he also recruited Mr. Thune as a candidate in 2002, for a Senate race he narrowly lost to Democratic Senator Tim Johnson. ?John Thune happens to be somebody who I recruited to run in the last cycle when I was chairman of the National Republican Senatorial Committee,? he added. ?I campaigned in the last cycle in South Dakota on buses and in restaurants with John Thune.?

For his part, Senator Daschle is taking the controversy in stride.

He said he welcomed Mr. Frist's visit and the chance it gave the Senate Majority Leader to hear the concerns of South Dakotans.