YUMA, Ariz. (AP) _ A mortally wounded police officer shot and killed his assailant in a bus station shootout, and authorities Thursday searched for the gunman's younger brother, who also is wanted by officials in three other states.

Edward Neil Smith fled on foot after his brother, Donald, 30, and Officer Gary Maas died in the gunbattle late Wednesday, said police spokesman Officer John Jung.

Maas, who was wearing a bulletproof vest, was the first officer killed in the line of duty in the department's 72-year history, Jung said. He was shot in the head and pelvic area.

The brothers were being sought by authorities in Texas, Washington and Idaho either for questioning or on warrants issued in crimes ranging from robbery to a fatal shooting, officials said.

Yuma police had said the Smiths were twins, but Texas authorities said Edward Smith is a year younger than Donald.

The shooting occurred late Wednesday after the driver of a Greyhound bus on its way to Yuma from Seattle radioed that two passengers had been drinking and were creating a disturbance, Jung said.

At the depot, Maas, 28, approached two men later identified as Donald and Edward Smith, Jung said.

At least one of the men drew a weapon and fired, fatally wounding the five- year police veteran, Jung said. Maas fired his gun as he fell to the ground, killing the elder Smith.

Investigators were trying to determine if Maas had been shot with two guns, Jung said.

Police armed with shotguns, rifles and automatic weapons combed this southwestern Arizona city Thursday.

''Yuma County is one of the more desolate areas in the state,'' Jung said. ''I couldn't even begin to guess where the guy is hiding.''

In Texas, Arlington police spokesman Jim Willett said the Smiths were wanted for questioning in numerous crimes, primarily armed robberies. Attempted capital murder warrants for the pair also had been issued in the March 14 shooting of a gas station attendant in an argument over 95 cents, Willett said.

Witnesses said Donald Smith shot the clerk point-blank in the head, but the bullet only grazed the man's skull and he recovered, Willett said. Donald Smith also was convicted of murder in Dallas County in 1976 but was released after serving several years of a 10-year sentence, he said.

''We fear Edward is en route back here because, he has friends, acquaintances, ex-girlfriends that live in Arlington, Dallas and Fort Worth,'' Willett said. ''They've had a reign of terror going for about four or five days now.''

Garland, Texas, police investigator John Gaines said the Smiths were wanted for questioning in the robbery-murder of a convenience store owner.

In Spokane, Wash., Detective Lt. Gary Johnson said the brothers were sought for questioning in the robbery of a retired couple and a supermarket.

''What we know of them, they are desperados,'' Johnson said.

In Cascade, Idaho, Valley County Sheriff M. Blair Shepherd said the brothers were sought for questioning in the death of an 20-year-old airman who was found fatally shot in a car stolen from the Spokane couple.