WASHINGTON (AP) _ The FBI named a new on-scene commander for the Oklahoma City bombing case Thursday as it prepared for ``a longer-term investigative commitment.''

Dan A. Defenbaugh, 43, who was assistant special agent in charge of the FBI's Mobile, Ala., office until his recent appointment as an inspector at headquarters, will take over as inspector in charge of the FBI's day-to-day command structure in Oklahoma City.

The other major federal investigative agency, the Treasury's Bureau of Alcohol, Firearms and Tobacco, has named Chris Cuyler, assistant special agent in charge of its New York office, to manage its work on the case in Oklahoma City.

The Justice Department is still reviewing candidates for lead prosecutor in the case to take over from Merrick Garland, the principal associate deputy attorney general, who was sent from Washington the day after the bombing to head the federal team in Oklahoma City.

More than two dozen federal prosecutors have volunteered for the job and more than half a dozen have been interviewed for it. There remained a remote possibility Garland, a key department manager, might stay on.

Two ex-Army buddies, Timothy McVeigh and Terry Nichols, have been charged in the case, but investigators say they are settling in for a painstaking search for between two and four other suspects. One object of this search has been dubbed John Doe 2 and has been portrayed in three sketches drawn from witness accounts.

A veteran investigator and manager of violent crime, terrorism and bombing cases, Defenbaugh is an FBI-certified bomb technician and has traveled to more than 20 countries on international terrorism matters. In 1983, he received the attorney general's award for excellence in law enforcement.

Weldon L. Kennedy, who has led the FBI's crisis management team in Oklahoma City since April 19, will return to his duties as head of the FBI's Phoenix office, where a major portion of the investigation of McVeigh's background has been conducted. He will remain as overall field commander and provide guidance for the nationwide investigation.

The new structure is similar to that used in previous long-term investigations, such as the 1989 mail bombings in the South that killed a federal appellate judge and a civil rights lawyer.

``We will not rest until this crime against humanity is resolved,'' said FBI Director Louis J. Freeh.