An individual can be drunk, behind the wheel of a car and have the keys in the ignition and still not be guilty of drunk driving, the state Court of Appeals has ruled.

 In a unanimous decision, the judges threw out the conviction of Vincent Zaragoza. They said the facts of the situation did not mean he was in “actual physical control’’ of the vehicle, which is what the law requires.

 The ruling, unless overturned, could alter how police deal with people who they believe are ready to drive while intoxicated but have not actually moved their vehicles.

 “It could put a lot of people in danger,’’ said Tucson Police Sgt. Fabian Pacheco. He said it undermines the ability of police officers to stop people who clearly are intoxicated from getting on the road in the first place.

 “These people that are in those situations are a step away from getting on the roadway and possibly killing somebody,’’ Pacheco said.

 And Tucson City Attorney Mike Rankin said the ruling “does give us cause for concern’’ in prosecuting cases with similar facts, where the person behind the wheel is not actually driving the car at that point.

 According to court records, a Tucson police officer observe Zaragoza walking toward a vehicle in a parking lot. He was unable to maintain his balance and hanging on to other cars.

 When the officer got to the car he said he observed Zaragoza sitting in the driver’s seat, with one hand on the wheel and th other putting the key in the ignition, though he had not started the vehicle. Zaragoza complied with the officer’s request to get out of the vehicle.

 A breath test indicated a blood alcohol content of 0.357. That compares with the legal presumption that someone is intoxicated at 0.08.

 Zaragoza later testified that he only intended to sleep in the car after having an argument with a companion. And he said he needed the key to roll down the windows.

 At his trial, Pima County Superior Court Judge Gus Aragon told jurors they could convict Zaragoza if they found he was in actual physical control of the vehicle. And the judge told jurors they had to decide that based on whether, considering “the totality o the circumstances, shown by the evidence, his potential use of the vehicle presented a real danger to himself or others.’’

 The jurors convicted him of aggravated drunk driving — his license had previously been revoked — and the judge sentenced him to four months in prison and put him on probation for five years.

 But appellate Judge Peter Eckerstrom said that isn’t what state law says.

 Eckerstrom acknowledged that the Legislature never has defined “actual physical control.’’ He said, though, that people cannot be convicted based on what they might be able to do in the future.

 “An impaired person in possession of car keys within a vehicle however motivated, always has the ‘potential’ to use the vehicle in ways that present `a real danger to himself or others at the time alleged,’ ‘’ Eckerstrom said. “But a person has not committed an offense until that person creates such a danger by actually physically controlling the vehicle.’’

 Prosecutors argued that the Legislature intended to allow police to stop drunk drivers before they actually drive. That, they said, made it necessary to criminalize the potential use of a vehicle while impaired.

 “But nothing suggests the Legislature intended to punish potential acts,’’ Eckerstrom wrote. “Rather, the language suggests it intended to punish actual behavior that creates a potential for harm.’’

 Rankin said the jury instruction the court found illegal is “substantially the same’’ as the ones given in cases with similar facts. He said if the decision is not overruled by the state

 Supreme Court prosecutors will have to come up with alternate jury instructions — ones that appellate courts find acceptable but potentially may make it harder to obtain a conviction.

 That presumes that police are able to make the arrest in the

 first place.

 “We’re going to continue to aggressively enforce DUI laws,’’

 Pacheco said. But he said officers will have to take into account the legal definition of what constitutes “actual physical control.’’

 Pacheco said it’s not unusual for those arrested on drunk driving charges to claim that they cannot be guilty because no one observed them actually driving.

 “We see many of those cases where people say, ‘I’m just going to stop here,’ or they leap-frog going home, stopping and then continuing on,’’ he said. “They have that potential to kill somebody.’’

 But Eckerstrom said the appellate court’s interpretation of the law also comports with other courtrulings which said the laws should be interpreted to encourage those who are intoxicated to pull over and sleep it off rather than keep driving.