H. Edward Tickel Jr., once considered the FBI's foremost expert in secret break-ins, was sentenced in federal court in Alexandria yesterday to eight years in prison for transporting stolen diamonds, obstruction of justice, tax evasion and two other charges.

"I'm remorseful, I'm sorry to cause all of these problems," Tickel, 42, told U.S. District Court Judge James C. Cacheris before he was sentenced. " . . . I've made some bad judgments."

A spokesman for the FBI said, "As far as we know, this is the stiffest sentence handed out to an agent convicted of criminal charges in the modern history of the FBI."

Tickel, who lives in Fairfax Station, has said he will appeal his convictions. According to defense lawyers, he will be eligible for parole in 30 months.

Immediately after yesterday's sentencing, Cacheris held a closed-door hearing on allegations, disclosed by the government, that Tickel had disclosed national security secrets to a former U.S. Senate aide. After the hearing, Cacheris raised Tickel's bond from $50,000 to $125,000.

Tickel, who has denied that he disclosed any government secrets, was immediately taken into custody by deputy U.S. marshals and as of last night was unable to post the bond for his release from jail. The prosecution has argued in court documents that Tickel's bond should be revoked because he is a risk to national security.

At the sentencing hearing, Tickel, seated at the defense table in the well of the courtroom, wiped his eyes as defense lawyers portrayed him as a solid family man with a lengthy record of service to his country.

An emotional plea for leniency for Tickel began when defense attorney Kenneth Michael Robinson approached the courtroom lectern, said a few words to Cacheris and then stood in silence for a full minute.

"Good people make mistakes . . . . If Peter could deny Christ three times, Ed Tickel could cover up a crime," Robinson told Cacheris.

Assistant U.S. Attorney John P. Hume, who has supervised the investigation and prosecution of Tickel, described the former agent as an "undercover criminal" since 1977, when the crimes for which Tickel was convicted began.

"He betrayed his office. He sold his office for criminal gain," Hume told Cacheris.

Tickel stood alone at the lectern as Cacheris sentenced him to jail on each of the six counts for which he had been convicted by a jury in March. The charges included one count of interstate transportation of stolen property, one count of tax evasion, two counts of obstruction of justice and two counts of false statements. Most of the prison terms are to run consecutively, adding up to a total of eight years.

In arguing against bond for Tickel, prosecutors have also alleged that during his trial Tickel had been driving a stolen van. The van was towed for a parking violation near the federal courthouse, impounded and then found by Alexandria police to be stolen. Robinson said he was convinced Tickel did not know the vehicle was stolen.

Robinson was unable to attend the closed-door hearing because he does not have federal security clearance. Defense lawyer W. Gary Kohlman had been granted such a clearance and was present for the session.

During his trial, Tickel, a 14-year FBI veteran, denied wrongdoing and said that he was the victim of a government "vendetta" because he had informed FBI Director William H. Webster that secret entries, known in bureau parlance as "black bag jobs," to install FBI eavesdropping equipment had been conducted without court permission.

A jury convicted Tickel on March 21 of transporting diamonds stolen from a North Carolina jewelry store in 1977 across state lines and related charges.

He was acquitted of six other charges.

Earlier this year, Tickel was acquitted of separate charges filed in federal court in Washington that he burglarized the FBI credit union in the J. Edgar Hoover Building.

Last Friday, he pleaded guilty to a misdemeanor charge that he had given four FBI radios to a stock car racing team in North Carolina. Sentencing on that conviction is set for Monday.