WASHINGTON, July 20 — The Senate voted overwhelmingly on Thursday to extend the landmark Voting Rights Act for another 25 years, as lawmakers of both parties said federal supervision was still required to protect the ability of minorities and the disadvantaged to cast ballots in some regions of the country.

“Despite the progress these states have made in upholding the right to vote, it is clear the problems still exist,” said Senator Barack Obama, Democrat of Illinois.

Approval of the measure, on a 98-to-0 vote, came on the day that President Bush made his first presidential visit to a convention of the N.A.A.C.P., where he promised to sign the bill.

The House passed the measure last week after a flurry of rebellion from several Southern lawmakers.

Republicans had made renewal of the law a cornerstone of party efforts to reach out to minority groups, particularly blacks, and leaders of both parties promised its passage in a rare joint event on the steps of the Capitol this year.