Former senator John C. Danforth, a Missouri Republican, emerged as the leading candidate yesterday to conduct an independent inquiry into the 1993 Waco siege, as Justice Department officials searched for a way to make the results of the investigation known publicly as soon as possible without jeopardizing potential criminal prosecutions, according to department officials and congressional sources.

A week after Attorney General Janet Reno began looking for an independent investigator to determine whether the FBI had tried to cover up facts related to the fatal fire that ended the 51-day standoff, she told reporters yesterday that the process has proved time-consuming because "I want to ensure that any individual has no conflicts, would be well-received and has the time to handle the task."

Justice Department officials have been in touch with Danforth, an Episcopal priest and former state attorney general, since mid-week to determine whether he could break away from his St. Louis law practice to take on the Waco investigation. An extensive background check to determine whether Danforth had any possible conflicts of interest is underway.

A three-term senator who retired in 1994, Danforth is best known as Justice Clarence Thomas's sponsor and chief defender during Thomas's bruising Supreme Court confirmation battle.

Although Danforth has agreed in principle to take the assignment, no formal announcement is expected from Reno until after Labor Day, Justice officials said last night. At least one other candidate was being vetted in case something unexpected developed to disqualify Danforth.

Reno acknowledged last week that her own credibility had been damaged by revelations that the FBI for six years had failed to produce potentially important evidence regarding the events near Waco, Tex., on April 19, 1993, when about 75 members of the Branch Davidian cult died. And in a startling gesture Wednesday, Reno authorized U.S. marshals to march into FBI headquarters to take possession of some of that evidence.

During her weekly news conference yesterday, Reno disparaged news reports of growing tensions between the Justice Department and the FBI, insisting that FBI Director "Louis Freeh and I have what I think is one of the best relationships that people can have in law enforcement."

Ultimately, Reno said she hopes that the independent investigation will restore public confidence. But accomplishing that aim poses a legal challenge that Justice officials were still trying to sort out yesterday. Reno said she expected the probe would begin as an administrative review rather than a criminal probe so that as much information as possible could be made public quickly. Testimony brought before a criminal grand jury is covered by strict rules of secrecy and often remains under wraps for years.

However, important administrative reviews--which can result in people losing their jobs but not going to jail--typically involve broad grants of immunity to employees who are compelled to testify as part of their jobs. So, for example, the FBI agents who fired the incendiary military tear gas canisters at the Waco compound on that last day could be required to speak to an administrative investigator--but in return, could generally expect grants of immunity because they would essentially be giving up their rights to avoid self-incrimination.

While such grants of immunity are commonplace, in this case a senior Justice Department official said, "precluding criminal investigation from the get-go would create a firestorm of protest." Department lawyers were developing procedures yesterday so that FBI and Justice Department personnel could be questioned without blanket grants of immunity.

To complicate matters further, Republican committee chairmen in both the House and Senate are launching their own investigations--efforts that raise the possibility of congressional grants of immunity. Justice officials hope that congressional Republicans might back off if someone of Danforth's stature is handling the inquiry.

Echoing this sentiment, Julian Epstein, Democratic staff director of the House Judiciary Committee, said that "if Danforth accepts it will defuse most if not all of the political momentum for investigative alternatives."

A GOP staffer, however, said that while Danforth is highly respected among Republicans, congressional inquiries would continue undeterred even if the former senator is appointed to head an investigation.