WASHINGTON (CNN) -- Senate Majority Leader Harry Reid promised to "reach across the aisle" as Democrats took control of the Senate on Thursday, but warned members they would be expected to work longer hours in the next two years.

"We found that a one-party town simply doesn't work," Reid, D-Nev., said in his first address to the chamber as majority leader. "We know from experience that majorities come and they go. We know that majorities are very fragile, and majorities must work with minorities to make that lasting change."

The Democrats won control of both Houses of Congress in November's congressional elections, but the party holds just a 51-49 edge in the Senate.

Reid said that slim margin provides a "unique opportunity" for bipartisan cooperation. And he promised to work with President Bush in the Democratic-led chamber, "or jointly we do nothing."

Reid said senators should prepare for "real work days" ahead, criticizing the workload taken on by the previous Congress.

"Factory workers, shopkeepers in America's malls, schoolteachers, police officers, miners, welders and businessmen and women work at least five days a week," he said. " Shouldn't we, here in Washington, where we do our business in the laboratory we call the United States Senate?"