Senator Clinton will square off against her long-shot Republican challenger in two debates this weekend, in what could be a dress rehearsal for 2008, when many think she’ll run for president.

While Mrs. Clinton has indicated that she will do little more than talk to voters to prepare for her current challenger, John Spencer, the debate could serve as an important political test for the junior senator.

With poll numbers suggesting the former first lady will win the Senate race in a landslide, Mr. Spencer has little to lose by aggressively grilling her on issues she has walked a fine line on, such as the war in Iraq.

A spokesman for Mr. Spencer, Robert Ryan, said the former Yonkers mayor will demand that Mrs. Clinton answer questions about the Patriot Act, National Security Agency wiretapping, and a host of other issues. Mr. Spencer, he said, was in Washington yesterday to talk policy with several people in preparation for the debate.

“John is going to be asking a lot of hard questions on where she stands on the issues,” Mr. Ryan said. “She has a lot of questions to answer, including, if elected will she serve out her term?”

Political analysts said that as a seasoned and disciplined politician who has been in the limelight for more than three decades, Mrs. Clinton is not likely to get ruffled by Mr. Spencer’s attacks.

This weekend’s Friday night and Sunday morning television slots are not peak viewership periods, but her comments from the debate can easily be hauled out after the debate and used against her.

And, the last thing she wants to do, political analysts say, is give her future opponents fodder. As the presumed Democratic frontrunner for 2008, her opponents will likely be hitting her from the political left and the right.

“While this debate might add to her battle readiness, it is not even remotely the same magnitude of the debates she’s going to be engaged in, in 2008 if she decides to run,” the executive director of RealClearPolitics.com, Tom Bevan, said.

A professor of public administration at Columbia, Steven Cohen, said one of Mrs. Clinton’s toughest challenges this weekend will be appealing to moderate and conservative voters while keeping her liberal Democratic credentials intact.

“She has to appeal to the blue state voters of New York at the same time that she has to appeal to the red state voters in the rest of the country,”Mr. Cohen said. “Whenever she’s doing anything in public that’s an issue for her.”

Lately she has been attacking the Bush administration on everything from the war to stem cell research. But debating Mr. Spencer could make “it harder for her to appeal to the base Democratic constituency” when she starts running a primary, Mr. Cohen said.

The editor of the Cook Political Report, Jennifer Duffy, said unlike Rick Lazio, who was in a tight race with Mrs. Clinton in 2000, but lost steam after aggressively going after her during a debate, Mr. Spencer can afford to be overly antagonistic because he has little chance of winning. Mr. Lazio approached Mrs. Clinton’s podium during the 2000 debate and demanded that she sign a document committing to ban soft money from the campaign. Some saw it as menacing.

Mrs.Clinton has thus far played it cool.

Yesterday, after a campaign event at a middle school on Long Island, she was asked whether she had started preparing for the debates.”I will,”she said, explaining that more important was getting out and talking to her constituents about other things.

The 7 p.m. Friday night debate will air on NY1 and other Time Warner stations.The 9 a.m. Sunday debate will be on WABC.