A federal jury yesterday convicted former FBI break-in expert H. Edward Tickel Jr. on six counts of obstructing justice, tax evasion and dealing in diamonds allegedly stolen from a North Carolina jewelry store in 1977.

The jury, which had been deliberating since last Tuesday in U.S. District Court in Alexandria, acquitted Tickel on six other charges, including allegations that he encouraged witnesses to lie to a federal grand jury.

Tickel, 42, a 14-year FBI veteran and expert in surreptitious entries who took part in some of the bureau's major cases, faces up to 35 years in prison and fines totaling $50,000. Judge James C. Cacheris set sentencing for April 15.

Tickel looked stunned as the verdict was read yesterday morning. The curly-haired ex-agent had spent much of last week joking with his guitar-playing defense lawyer, Kenneth Robinson, as the two men waited in Robinson's car for the jury's decision.

Tickel was acquitted recently in the District of Columbia of a separate charge that he burglarized the credit union office at FBI headquarters.

Tickel took the witness stand during the Alexandria trial to deny any wrongdoing. He maintained the charges were part of a vendetta aimed at him after he informed FBI Director William H. Webster that secret entries to install eavesdropping equipment had been performed without court authorization.

Webster, called as a government rebuttal witness, testified that "no one, including Mr. Tickel, ever talked to me about an illegal entry" in the two cases cited by Tickel.

One of the cases allegedly involved an entry into the Chicago hotel suite of then-Teamsters vice president Roy Lee Williams in November 1979. Williams was convicted four months ago of conspiring to bribe Sen. Howard Cannon (D-Nev.).

In the second case, Tickel said he made an unauthorized entry at a Louisiana hunting lodge belonging to reputed New Orleans Mafia chief Carlos Marcello. Tickel testified he originally believed both entries were legal, but was told later that court orders had not been obtained.

In his closing argument last week, defense lawyer Robinson scoffed at the charges facing his client, claiming that Tickel's knowledge of FBI surveillance targets was "priceless."

"If he's corrupt, he'd sell information for millions--not diamonds for thousands," Robinson said.

Assistant U.S. Attorney John Hume told the jury Tickel had left a "trail of evidence . . . . What you see is omission, evasion, deception, lies. Nothing he said from that stand makes sense for an FBI agent."

Tickel, who still faces trial in the District on charges he gave FBI radios to the Richard Petty racing team in North Carolina, said he was certain to appeal.