WASHINGTON, Nov. 5 — President Bush on Sunday seized on the conviction of Saddam Hussein as a milestone in Iraq, seeking to rally Republican voters with the issue of national security as some polls suggested that his party might be making gains in the final hours of the campaign.

The White House said the timing of the announcement, two days before Election Day, had nothing to do with American politics and had been dictated by the Iraqi court. But Mr. Bush moved quickly to put it to use in what has been his central strategic imperative over the past week, trying to rouse Republican voters to turn out.

“Today we witnessed a landmark event in the history of Iraq: Saddam Hussein was convicted and sentenced to death by the Iraqi High Tribunal,” Mr. Bush said to roars of approval in a hockey auditorium packed with supporters in Grand Island, Neb. “Saddam Hussein’s trial is a milestone in the Iraqi people’s efforts to replace the rule of a tyrant with the rule of law.”

The announcement out of Baghdad came as polls suggested some gains for Republicans. A Pew Research Center Survey released on Sunday found that the number of likely voters who said they would vote for the Democrats was now 47 percent compared with 43 percent who said they would vote for Republicans. Two weeks ago, Democrats had an edge of 50 to 39. A Washington Post-ABC News poll found a similar tightening.

These kinds of polls, about the so-called generic ballot, measure national trends and do not necessarily provide an accurate measure of what is happening in individual House and Senate races. Andrew Kohut, the president of the Pew Center, said the poll nonetheless found that Republicans were becoming more enthusiastic as Election Day approached, a sign that the party was making progress in addressing one of its main problems this year: a dispirited base.

With at least 20 House races and 3 Senate races virtually tied in polls over the past week, Republican officials have looked to the huge voter turnout operation the party has developed over the past six years as its last-stand defense to prevent Democrats from making big gains on Tuesday.

A series of Mason-Dixon polls published on Sunday suggested a tightening in two Senate races, Rhode Island and Maryland, that Democrats had been confident of winning.

Republicans over the past week have spent heavily in Maryland on behalf of Michael Steele, the Republican candidate seeking to fill the seat being vacated by Senator Paul S. Sarbanes, a Democrat. In Rhode Island, Senator Lincoln Chafee, the Republican, has spent heavily and banked on his family’s long history in the state’s politics to help him survive in a heavily Democratic state.

Ken Mehlman, the Republican chairman, said polls showed that Republicans and conservatives “were coming home,” which he said “is what happens when voters focus on the choice before them.”

Representative Rahm Emanuel of Illinois, the Democrat leading his party’s effort to win control of the House, said, “It’s inevitable that there would be some tightening in the end.”

Still, Mr. Emanuel, who has been careful this campaign to avoid the public expressions of optimism voiced by other Democrats, added, “This is making me nervous.”

Across the country, Democrats also hailed the verdict in Baghdad but argued that it would make no difference in delivering stability to Iraq and would have little bearing on Tuesday’s vote.

“I think it’s a great verdict — I mean, Saddam Hussein is a war criminal and he’s getting what he deserves,” Howard Dean, the Democratic national chairman, said on “This Week” on ABC. “But I don’t think it has any impact on the safety of America.”

Representative John P. Murtha, the Pennsylvania Democrat who has become the face of his party’s opposition to the war in Iraq, said the verdict was the right one but predicted it would not make a difference in this campaign. What would matter more, Mr. Murtha said, were editorials in military papers being published Monday calling for the resignation of Defense Secretary Donald H. Rumsfeld.

“When The Army Times, The Navy Times, The Marine Corps Times, they have all said that we’re not supporting the troops, that they’re losing confidence with the administration, that’s what’s important,” Mr. Murtha said, campaigning in Croydon, Pa., outside Philadelphia, for Patrick Murphy, a Democrat seeking to unseat Representative Michael G. Fitzpatrick.

The fact that Mr. Bush was spending this last Sunday before Election Day in two of the most Republican states in the nation was testimony to how bleak a year this has been for the Republican Party and the president. And in Florida, the home state of his brother, Mr. Bush received what appeared to be another reminder of his political unpopularity when Charlie Crist, the Republican candidate for governor, backed out of a planned appearance with Mr. Bush in Pensacola on Monday.

Mr. Crist said that he needed to spend the day in more competitive parts of the state and that he was not joining the list of other Republican candidates who had snubbed Mr. Bush this year.

Tuesday May Bring Bush Worry Either Way Fight for U.S. Congress focuses on turnout