Real bipartisanship is not a mathematical formula, it is a spirit

Senate Majority Leader Tom Daschle

"The majority is slim. This is still one of the most closely divided senates in history," Democrat Tom Daschle from South Dakota said in his opening speech in his new role.

"Real bipartisanship is not a mathematical formula, it is a spirit. It is a way of working together that respects differences."

The Republican Party formally ceded control of the Senate following the decision by one of its senators to become an independent. It gave the Democrats a one-seat majority.

I do think we have made a difference to the country over the past six years

Minority Leader Trent Lott

The Republicans had controlled the chamber since 1995.

Democrats are now taking the helm in the full Senate and each of its committees.

They are expected to challenge President George W Bush's conservative agenda.

Formalities

Mr Daschle was presented as majority leader after the traditional prayer and pledge of allegiance.

Mr Bush will have a harder time getting Senate support

Senators then adopted a resolution appointing the most senior Democrat, 83-year-old Robert Byrd from West Virginia, as the new president pro tempore.

He replaces veteran Republican Strom Thurmond, a South Carolina senator, in the mainly ceremonial post.

Mr Daschle followed with his introductory speech, in which he pledged to be constructive in putting through legislation.

"At a time when Americans are evenly divided in their choice of leaders, they are united in the demand for action," he said.

New agenda

Mr Daschle was welcomed by his predecessor, Republican leader Trent Lott, who praised his party's own record in the majority and vowed to pursue President Bush's agenda.

Mr Jeffords became an independent, supporting the Democrats

"I do think we have made a difference to the country over the past six years," he said.

When the Republicans controlled the agenda in the Senate, Mr Bush had wanted the upper house to move from income tax cuts to his missile defence and energy plans and possible business tax breaks.

But the newly configured chamber will instead push ahead with a patients' bill of rights, an increase in the federal minimum wage and a prescription drug benefit under Medicare.

Political milestone

The power change occurred following the switch by Vermont Senator James Jeffords.

Mr Jeffords took his seat with the Democrats. His desk was moved across from the Republican side before Wednesday's session.

BBC Washington correspondents says it is a political milestone - the first time control of the Senate has changed without an election.

Republicans retain their grip on the House of Representatives, by 221 to 209, with two independents and three vacancies.