Jon C. Vasilacopulos, the Utah man who pleaded guilty in 1984 to conning investors in a diamond scheme, could soon be back on the street thanks to a Utah Court of Appeals ruling invalidating his guilty plea.

Judge Russell Bench, writing for the unanimous three-judge panel, said Vasilacopulos was not told, as required by law, that he could get consecutive terms when he pleaded guilty in 1986."The trial court clearly failed to find defendant understood the possibility of consecutive sentences," Bench wrote. "The state argues the rec-ord as a whole affirmatively established defendant's full awareness of such a possibility. We disagree."

The ruling, if it stands, would mean Vasilacopulos is essentially back where he was before the plea bargain - a defendant awaiting trial on 20 counts of theft by deception. As such, he may well ask to be released from the Utah State Prison, where he was due to stay until his parole date of 1994.

And, in fact, his attorney, James N. Barber, contemplates doing just that.

"He'll get out of prison as if he was never tried," Barber said.

Barber said, however, that Vasilacopulos will likely be remanded to the Salt Lake County Jail, where he will await trial unless he can post bail, which has yet to be set.

But Assistant Utah Attorney General Stan Olsen said he will request that Vasilacopulos remain behind bars while he asks the appeals court to reconsider its ruling. If the appellate judges decline - and chances are they will - Olsen said he will make the same request while appealing to the Utah Supreme Court.

Barber said he may oppose an attempt to keep Vasilacopulos in prison, although he said it may be appropriate to wait until after the judges rule on the petition for reconsideration.

Barber also suggested the attorney general's time and resources could be better used to prepare for trial, which he said must be held in a matter of weeks due to speedy trial requirements. However, he also did not rule out the possibility of further plea bargain negotiations.

"I think it's important to recall he's done quite a bit of time in prison, and it does raise the potential for a plea bargain," Barber said. "But I'm not suggesting he would enter another plea bargain. I don't know what he thinks on that."

Vasilacopulos was arrested in November 1981 and charged with 20 counts of theft by deception in a diamond investment scam. He later pleaded guilty to a second-degree felony and two third-degree felonies and was to be sentenced in August 1984. But he disappeared.

Almost a year later, Vasilacopulos was arrested in California and extradited to Utah. On Aug. 12, 1985, 3rd District Judge Homer Wilkinson imposed a $20,000 fine and sentenced Vasilacopulos to 1-to-15 years on the second-degree count and 0-to-5 years on the third-degree counts. He also made the sentences consecutive instead of concurrent, which means one sentence must be served before the other begins.

In June 1986, Barber asked Wilkinson to let Vasilacopulos withdraw his plea because he wasn't told of the possibility of consecutive sentences. Wilkinson refused, but the appeals court reversed Wilkinson and ordered that Vasilacopulos be allowed to withdraw his guilty plea.