WASHINGTON (By Carl Hulse) January 1, 2004 - A more Republican and more conservative Congress convenes on Tuesday, with Republicans intending to use their greater strength in the House and Senate to help President Bush pursue a second-term agenda of major changes in bedrock programs like Social Security and income taxes.

"This is going to probably be the most productive two years of our Republican majority," said Tom DeLay of Texas, the House majority leader. "It's not just Social Security and tax reform, it's tort reform, regulatory reform, restraining spending, redesigning the House, redesigning the government."

Nine new senators and 41 House freshmen will be sworn in as the 109th Congress opens at noon on Tuesday, but the ceremony could be quickly overshadowed by a resumption of the sharp partisanship that was a hallmark of the Congress that ended last month.

In the House, the two parties are poised for an opening-day fight over a package of rule changes that Democrats and outside watchdog groups say are intended to dilute the power of the House Ethics Committee after it admonished Mr. DeLay three times last year. The rules package also contains an initiative to create a permanent Homeland Security Committee, an idea that has met with resistance from some senior lawmakers who would lose authority to such a panel.

Senators will quickly turn to confirmation hearings for Mr. Bush's second-term cabinet choices, beginning with the nominees to head the Justice, Agriculture and Education Departments on Thursday. Others will rapidly follow, with Senate confirmation votes possible soon after Mr. Bush is inaugurated on Jan. 20.

The House and Senate also expect to move fast on an aid package for the South Asian region devastated by last week's tsunami. "This is going to dominate the next couple of weeks," said Bob Stevenson, a spokesman for the Senate majority leader, Bill Frist of Tennessee, who along with other lawmakers intends to visit the region sometime in the next week.

The session will also be held against the backdrop of continuing violence in Iraq and the need to provide billions of dollars to sustain the military effort there, in Afghanistan and elsewhere.

Senate Republicans gained four seats in the November elections, enlarging their majority to 55 to 45 and putting them closer to the 60 votes needed to break filibusters. The seven new Republican members include a core of fiscal and social conservatives moving across the Rotunda from the House who are strongly against abortion and for tax cuts.

Dr. Frist has indicated that he intends to use his enhanced majority to try to cut off Democratic filibusters of the president's judicial nominees by whatever means necessary, a threat that if carried out could ignite partisan warfare. Dr. Frist and Senator Harry Reid of Nevada, the new Democratic leader, are also wrangling over how to divide money for committee staff and resources.

Democrats in both chambers express a willingness to work with Mr. Bush and the Republican leadership, but say they will not be overpowered by majorities determined to push through an objectionable agenda or controversial nominees.

"Republicans control both the House and the Senate," Mr. Reid said in a statement. "They will establish the agenda, and they will decide if this Congress will work in a bipartisan fashion or be defined by partisan debate."

In the House, Republicans - bolstered by a contentious redistricting in Texas - gained three seats for a new majority of 232 to 202, with one independent who generally votes with the Democrats. Republicans have increased their numbers for two straight elections, a trend House Democrats will try to reverse in the 2006 midterm contests.

But there is a significant amount of business to be conducted between now and then, and consensus could be elusive. Leading Democrats and allied interest groups are especially leery of the Republican push on Social Security. They also feel that Republicans have cut them out of the legislative loop for the most part, in the House particularly, an assertion denied by Mr. DeLay.

"If they want to play, they need to come to the table," Mr. DeLay said. "Whenever we have invited them to the table, if they take an advantage of it, at the very end, they always turn and run."

In some respects, Mr. DeLay's fellow Republicans may pose a bigger threat to the party's agenda than the Democrats. Now that Mr. Bush has been re-elected, some Republicans have shown a willingness to buck the White House in the fight over the intelligence reform measure. Other Republicans are already balking over proposed Pentagon cuts as a way to reduce the deficit. Still others hope to overcome administration and leadership resistance to allowing cheaper drug imports.

Lawmakers still have some business remaining from the last session, with a highway measure among the major holdovers. Congressional Republicans and the White House were unable to come to terms in 2004 over the cost and chose to extend current spending rather than engage in a veto fight. But lawmakers in both parties would like to start that money flowing.

Bolstered by the new majorities, lawmakers involved in energy policy would also like to shake free a long-stalled energy measure that provides incentives for new domestic oil and gas production as well as money for research into new sources of fuel. Republicans say they may now have the votes to win approval for drilling in the Arctic National Wildlife Refuge, which has long been opposed by national environmental groups and most Democratic lawmakers. And a coalition of Republicans and Democrats hopes to change campaign spending laws to restrict the third-party advertising efforts that were so prevalent in this year's elections.

The Congress will include some new faces with familiar names, with the offspring of four former members elected to House seats: the Republican Connie Mack of Florida and the Democrats Dan Lipinski of Illinois, Dan Boren of Oklahoma and Russ Carnahan of Missouri.