(second paragraph should say Baucus is the eighth senator and sixth Democrat)
WASHINGTON, April 23 (Reuters) - U.S. Democratic Senator Max Baucus of Montana, chairman of the powerful Senate Finance Committee, will not seek re-election to a seventh term next year, a Democratic aide said on Tuesday.
Baucus, 71, first elected to the Senate in 1978, will become the eighth senator - six Democrats and two Republicans - to announce plans to retire at the end of next year.
Baucus' office had no immediate comment on his plans.
Democrats currently have a 55-45 majority in the Senate. Former Montana Democratic Governor Brian Schweitzer is a leading contender to run for Baucus' seat.
Baucus' Senate Finance Committee is currently working to revamp the U.S. tax code. He played a key role in President Barack Obama's landmark overhaul of the U.S. healthcare system, which was signed into law in 2010.
Baucus' decision not to seek re-election did not come as a surprise to many fellow Democrats who knew that the remarried senator was considering retirement, aides said.
If Democrats retain the Senate in next year's election, Democratic Senator Ron Wyden of Oregon is next in line in party seniority to replace Baucus as Finance Committee chair. (Reporting by Thomas Ferraro and Kim Dixon; Editing by Bill Trott)