Starting Jan. 1, authority for investigating many felonies on the Navajo Reservation will shift to the tribal police department from the federal Bureau of Indian Affairs.

Tribal Chairman Peter MacDonald last week signed an agreement that will give tribal police investigators jurisdiction over such felonies as assault and rape.The FBI will continue to investigate some major felonies on the reservation, including murder and armed robbery.

Results of the felony investigations will be turned over to the U.S. attorney's office for prosecution in the federal courts.

The agreement does not affect the tribal courts, which have authority only to try misdemeanors.

"This agreement alleviates many of the barriers that have constrained tribal police in investigating crimes committed here on Navajoland," MacDonald said. "A crime can now be investigated and followed through to prosecution."

However, tribal Police Chief Bill Kellogg said the transfer of power will, in some ways, have little effect on the tribal police department's investigation policies.

"We have been investigating these crimes all along," he said.

In the past, tribal investigations were conducted in conjunction with the BIA investigations because of the possibility that no federal prosecution would be undertaken. Then the cases were taken to tribal court and prosecuted as misdemeanors.

The success of the increased jurisdiction for the tribe will depend on how many cases the U.S. attorney's office agrees to prosecute, said James Stevens, the Navajo area's BIA director.