WASHINGTON—On a recent Saturday morning in a hardscrabble neighborhood here, a stocky man who could not afford a lawyer attended a legal clinic to ask a question about his mother's will.

His case was assigned to a Justice Department employee in jeans and a red sweater, one of about 20 volunteers that day. After hearing the query, the employee said he needed to look up the law of wills and trusts.

“;Aren't you a lawyer?”; the man asked suspiciously.

The employee—Laurence H. Tribe, a Harvard Law School professor who is arguably the most famous constitutional scholar and Supreme Court practitioner in the country—assured the man he was, and then went off in search of a working Internet connection.

For Tribe, volunteering to answer routine legal questions was a show of grass-roots support that grew out of his new role at the Justice Department, where the 68-year-old liberal legal icon—who is also President Barack Obama's mentor and former teacher—is now the “;senior counselor for access to justice.”;

In that position, created especially for him, Tribe has been asked to suggest ways to improve legal services for the poor, find alternatives to court-intensive litigation and strengthen the fairness and independence of domestic courts. But Tribe has a small staff, a limited budget, little concrete authority and a portfolio far less sweeping than the one he told friends he had hoped to take on in Washington.

He is also largely invisible. The Justice Department is not allowing him to give interviews, apparently in part because of nervousness in the administration that his unabashedly liberal views might draw criticism or that Tribe, described by friends as having a big intellect and a healthy ego, might stray from his assigned lane.

One friend and fellow Harvard law professor, Charles J. Ogletree, said he was thrilled that someone of Tribe's prominence was working on indigent defense issues. Still, he said Tribe had not been given responsibilities commensurate with his abilities and expressed hope that that would change.

“;He's capable of doing a lot more than he'll probably be asked to do,”; Ogletree said. “;My sense is that once the administration gets a sense of how remarkably creative Larry can be in advancing the Justice Department's agenda and that of the president, they will not hesitate to utilize his considerable talents.”;

Ogletree said he was confident that in the meantime, Tribe would make good use of “;the bully pulpit of reason and urgency to talk about improving our criminal justice system.”;

The Justice Department said Tribe could assume a more public role in the future, noting that his initiative was still new and that he was still figuring it out. And Thomas C. Goldstein, a prominent Supreme Court lawyer who has worked with Tribe for more than a decade, said Tribe had described himself as happy and busy with the job, which he assumed in March.

Tribe was one of Obama's earliest supporters, appearing in a campaign commercial and telling colleagues he hoped to work for him after the election. And, friends say, events in Tribe's personal life—including a brain tumor and a divorce—heightened his desire to leave Cambridge for a while and to try something new: public service.

Obama himself made clear that he wanted to find a place for Tribe, according to interviews with administration officials who would speak only on the condition of anonymity. But for those putting together the staff, figuring out what to do with Tribe was difficult.

Admirers and detractors alike say that no law professor of his generation has had greater influence; many believe he would be a Supreme Court justice today had he not earned enduring Republican enmity by leading academic efforts to portray Robert H. Bork as an outside-the-mainstream conservative when he was nominated to the Supreme Court in 1987. (Bork was not confirmed.)

For that reason, officials decided that Tribe could not be given a position that would require Senate confirmation, like solicitor general, because Republicans would probably go to war against him, with decades of legal writings to mine for ammunition.

There was also concern over how his presence might play out internally, several administration officials said. Some officials feared that he might be unmanageable, intruding into all manner of policy areas and able to call on Obama as a trump card.

“;He has an ego,”; said Charles Fried, a former solicitor general in the Reagan administration and a fellow Harvard law professor. “;He's entitled to it. He's earned it.”;

Several friends and administration officials said Tribe had initially sought and believed he would be given a far broader title and assignment: counselor for “;rule of law”; issues, which would have come with a mandate to help shape matters of national security and foreign policy. That did not happen, but Tribe came to Washington anyway.

Still, several of his Harvard colleagues noted that he may wield unofficial influence because of relationships with former students and proteges throughout the government—not least with Obama.

“;When the president of the United States respects your views, that conveys more authority than a title,”; said Alan M. Dershowitz, a Harvard law professor.

Attorney General Eric Holder, for one, has said he is grateful for Tribe's presence. When Holder gave a recent speech before a group that urges lawyers to do pro bono work, he took Tribe along and pointed him out, lauding his initiative as a landmark expansion of the department's efforts to improve access to legal services.

Some advocates for indigent defense, though, are skeptical that the administration's use of Tribe is a sign of a concrete commitment to that issue. Among them is Virginia E. Sloan, president of the Constitution Project, a bipartisan legal advocacy organization, who noted that Tribe had no authority to overhaul the Justice Department's law enforcement grants to states to require greater spending on public defenders.

“;The question is what kind of influence he is going to have in the department,”; Sloan said. “;Can Larry Tribe make it happen? If you look at his resume, he's never been out of academia, so how is he going to move DOJ. when very savvy people with government experience have been trying for months to get them to do something and have failed?”;

Tribe's friends said that if he felt he could not do something meaningful in Washington, he would quit.

“;If Larry Tribe is in any way viewed as—or is in fact—only window dressing,”; Ogletree said, “;then I have no doubt that he would resign from that position and return to Cambridge in a New York minute.”;