(Updates with details)

By Thomas Ferraro and Richard Cowan

WASHINGTON, Jan 6 (Reuters) - Democrats sealed their increased control of the U.S. Congress on Tuesday with the swearing in of newly elected members expected to help enact President-elect Barack Obama's call for a massive economic stimulus package.

Gavels sounded at about noon EST (1700 GMT), opening the Senate and House of Representatives a day after Obama visited Capitol Hill to press for quick action on a $750 billion package of tax cuts and new spending designed to stem a deepening recession.

Obama takes office on Jan. 20, giving Democrats control of the White House, the House and Senate for the first time in 14 years.

Vice President Dick Cheney, in his final days as Senate president, swore in the newly elected senators as one of the first orders of business.

Despite such challenges as the economy, two wars and an estimated 46 million Americans without health insurance, the opening day of Congress was something of a victory party for the Democrats.

Yet the celebration was muted by a flap over a pair of seats that remained empty in the 100-member Senate.

Senate Democrats refused to swear in, at least for now, a fellow party member, Roland Burris of Illinois. He was appointed to fill the seat vacated by Obama by a governor engulfed in scandal, but the secretary of the Senate rejected his credentials as incomplete amid controversy over the appropriateness of the appointment.