WASHINGTON – Democrats yesterday rallied around the notion that President Bush’s nominee to be chief justice of the United States, Judge John Roberts Jr., is too much of a gamble to confirm because of what they described as a growing concern that he lacks the heart to be trusted with ensuring the rights of minorities, women, and the poor.

In the last day of questioning from the Senate’s judiciary committee, Democrats acknowledged the nominee’s skills as a thinker and his stamina in fielding nearly 20 hours of questions, many of them hostile, with fluidity and charm. But many, including the party’s chairman, raised the possibility of a party-line vote because of questions about the nominee’s commitment to civil rights and legalized abortion.

Senator Schumer of New York summed up the frustration of Democrats by failing to coax incriminating statements from Judge Roberts by using the last minutes of his allotted time asking the nominee what he would ask himself if he were on the committee. It was a startling act of resignation from Mr. Schumer, whose compliments of Judge Roberts were so effusive as to prompt the nominee to thank him when the questioning period was over.

“You’re one of the best litigators in America,” Mr. Schumer said. “You know how to convince people. That’s what you’ve been paid to do for a long time. So let me ask you, if you were sitting here, what question would you ask John Roberts so that you or us could be sure that we weren’t nominating what I call an ideologue, someone who you might define as somebody who wants to make law, not interpret law?”

Senator Durbin, a Democrat of Illinois, raised a similar concern when Judge Roberts told him he would likely have argued the other side in a case he once won on behalf of a client who was challenging a Colorado law that limited gay rights.

“If this is just a process, a legal contest, and you’ll play for any team that asks you to play,” Mr. Durbin said, “it raises a question about where would you draw the line, if you would ever draw the line.”

The nominee’s response to Mr. Durbin crystallized two views of the law that played out throughout the hearing – the view of Judge Roberts that a dispassionate reading of the law is the best guarantee of rights for all, and the view of some Democrats that judges have a special obligation to the underdog when resolving legal disputes.

“If the Constitution says the little guy should win, the little guy’s going to win in court before me,” Judge Roberts said. “But if the Constitution says that the big guy should win, well, then, the big guy’s going to win, because my obligation is to the Constitution. That’s the oath.”

That Democratic opposition to Judge Roberts had hardened throughout the day became clear when the chairman of the Democratic National Committee, Howard Dean, posted a letter that echoed the sentiments of some judiciary committee members on the party’s Web site that was expected to be widely distributed today.

“Judge Roberts is said to love the law, but loving the law without loving the American people enough to protect their individual rights and freedoms will make our American community weaker,” Mr. Dean said. “And the exercise of the law without compassion … undermines the grace and wisdom of the founders whose sense of balance and fairness made this country great.”

Judge Roberts is expected to be approved along party lines in a judiciary committee vote next Thursday and by the full Senate before the Supreme Court resumes on October 3. In a concession to his qualifications, some expect that he could win the vote of at least one Democrat on the committee. Some have predicted he could earn a handful of Democratic votes in the full Senate by senators whose states voted for President Bush last year.

Judge Roberts challenged the impression among some Democrats that he is a hired gun by tentatively agreeing that the Reagan administration overstepped its authority by funneling money to the Contras, but fortified it by declining to distance itself from any of President Reagan’s official policies. He challenged the view when he agreed that defense lawyers occasionally abuse the system, but fortified it by noting that abuses occur on the other side too.

Mr. Bush nominated Judge Roberts to replace Justice Sandra Day O’Connor, then nominated him as chief justice when Chief Justice William Rehnquist died earlier this month. The president is expected to nominate a replacement for Justice O’Connor in the coming weeks.