Washington ? John Roberts is on track for a seat on the Supreme Court barring a misstep at hearings beginning Tuesday, according to supporters and critics who say the coming confirmation debate will test Senate Democrats as well as the nominee.

Relatively few Republicans and no Democrats have formally announced how they will vote on the nomination of the 50-year-old appeals court judge, saying they first want to follow the hearings.

Behind the studied show of neutrality, though, several Republicans who are tracking Roberts’ nomination say he already has the likely support of all but two or three of 55 GOP senators and perhaps a few Democrats – enough to assure confirmation unless liberals launch a filibuster.

Sen. Arlen Specter, R-Pa., has pledged to preside over “efficient, dignified” hearings as chairman of a Judiciary Committee known for outbursts of unruly partisanship. At the same time, the Pennsylvania Republican said senators and the country “need to know much more” about Roberts’ judicial philosophy.

President Bush named Roberts in July as the court’s first new justice in 11 years. If confirmed, he would succeed Sandra Day O’Connor, who has often cast a deciding vote on abortion, affirmative action and other issues.

Conservatives, eager to have the court take a new direction, swiftly embraced Roberts when Bush appointed him.

Given the political backdrop, Democrats, as well as the liberal groups that have already announced their opposition to the nomination, hope to use the hearings to flesh out Roberts’ judicial philosophy and views.

The Democratic objective “is to figure out what kind of justice John Roberts will be,” Sen. Charles Schumer, D-N.Y., said in a recent interview. “Will he be an ideologue who imposes his views on everyone through the courts, or will he be a mainstream justice, albeit a conservative one?”

The Republicans who described support for Roberts do so on condition of anonymity, saying they were not authorized to speak about vote counts. If either Democrats or their customary allies disagree with that assessment, they have not said so, and their own actions lend them credence.