CHEYENNE, Wyo. (AP) - People whose blood-alcohol content registers below the state's legal limit of 0.08 percent account for about one in 30 of a prosecutor's driving under the influence cases.

The reason people who test below the legal limit can still be charged is a little-known state law that allows other factors to be taken into account, such as a suspect's ability to walk a straight line.

One case was the arrest of Johnny Alegria, 35, of Wheatridge, Colo., who was pulled over after he was allegedly clocked at 106 mph.

The arrest report shows a breath test result of 0.06 percent. Also, Alegria allegedly smelled of alcohol and could not count backward from 67 to 54, according to Wyoming Highway Patrol Trooper Shane Swilling.

Police trained in identifying drunken drivers can arrest "barely drunk" drivers so long as there is evidence of impairment, Laramie County prosecutor Dennis Grant said.

In his seven years as a part-time prosecutor, Grant has been assigned most of the county's DUI cases. He said drivers who blow 0.08 or greater on the breath test are, in almost every case, a slam dunk for prosecutors.

But he concedes that those who slide under the breath limit are not so easy to convict.

After nine years of policing on F.E. Warren Air Force Base and five years with the Cheyenne police, officer George Trammell said he is usually right about the breath test even before the driver takes a deep breath.

"You can get a conviction without a breath test," he said.

Did the driver correctly recite the alphabet start to finish, or successfully complete the heel-to-toe turn and walk? Was the driver's speech slurred?

Officers can make an arrest if they think someone should not be behind the wheel. But they then take on the burden of proof.

Trooper Duane Ellis said the totality of evidence must be considered. "Each section of the field sobriety test is weighted differently."

The effects of alcohol differ among people who drink.

"Some people can hold it better than others," Grant said. "The amount of alcohol consumed can be the same, and the concentration in the system can be the same, but the behavior different."

Ellis said people often argue with him about DUI.

"I've seen 0.06, and quite frequently, those drivers are all over the road," he said. Yet an experienced drinker can walk, talk and drive pretty well even at twice the legal limit.

AP-WS-05-31-04 1349EDT