Marvin Mandel's prision furlough ended yesterday, and the former Maryland governor headed back to a Florida prision camp, leaving behind a trail of questions about his treatment by parole officials.

Federal parole officials have ordered him to remain in prision until next May -- in essence, serving almost his entire term, despite recommendations by federal prosecutors that he not be forced to remain imprisoned for the full period.

Mandel's attorney asserted yesterday that the treatment is "discriminatory" in light of paroles granted to other prominent officials convicted of crimes involving public corruption. And several former prosecutors who have handled political corruption cases also said it appeared Mandel was being singled out for harsh treatment.

Bruce Bereano, one of Mandel's lawyers, pointed to the recent parole of former congressman Charles Diggs, who served less than nine months of a three-year prison term. He had been convicted of fraud in a $60,000 kickback scheme, in which he inflated the salaries of several staff members and then used the money to pay his own office and personal expenses.

"Here the crimes were as heinous, if not more heinous, than Mandel's," Bereano said. "It shows as clearly as anything the discrimination and different treatment."

Although he refused to discuss details of the cases, Benjamin Malcolm, the Parole Commission's acting chairman, denied the allegation and said "they are entirely two different cases."

"They may have been similar in nature. Bank robbers are similar in nature, but one may have a gun and one may not . . . so you can't lump them together," Malcolm said in the commission's first public comment on the Mandel controversy. "I would hope the public would have the idea that when a public official gets into difficulty, there are differences in offenses. They're not all going to get the same time [in prison]."

Last October, after Mandel and several of his codefendants were given differing parole dates, U.S. Attorney for Maryland Russell T. Baker Jr., whose office had prosecuted Mandel, wrote to the commission, saying that all the defendants should be treated the same and that there was no reason for them to serve their full terms.

Mandel's problems with the prison system were highlighted last night by his wife, Jeanne, who called reporters to say that the former governor had been placed in solitary confinement upon his return to the prison camp at Eglin Air Force Base because he had talked to reporters during his five-day furlough, spent at home in Annapolis.

Prison sources denied Mrs. Mandel's assertion and said Mandel had failed a routine "breathalyzer" test that detects alcohol on the breath. One of the conditions of any prison furlough, they said, in abstinence from alcohol. As a result of the test, according to the sources, Mandel was placed in a cell by himself away from the dormitory where he is normally housed in a cubicle.

Mrs. Mandel refused to belive her husband had been drinking. "He's not going to jeopardize himself by doing something like that," she said. She also said three inmates had called her from the prison to say Mandel's cubicle had been cleaned out by prison guards before he returned indicating that prison officials planned to place him in solitary. The prison sources emphatically denied that contention.

While Mandel has essentially been denied parole, a look at the parole records of several prominent officials convicted of wrongdoing shows that most were paroled months before their prescribed terms would have ended. White House aides H. R. Haldeman and John D. Ehrlichman, each sentenced to one to four year for their roles in the Watergate cover-up, were paroled after 18 months in federal prison camps. Former attorney general John N. Mitchell, convicted of perjury and other offenses in the same scandal, served 19 months of his one-to-four year term.

Former Oklahoma governor David Hall, convicted of using his influence to get favorable state action for a businessman who had agreed to pay him $100,000 for his help, was sentenced to a three-year prison term. He served 18 months, according to a spokesman for the Federal Bureau of Prisons.

Mandel and five codefendants were convicted in 1977 of mail fraud and racketeering -- charges stemming from naipulations to increase the vaule of a race track secretly owned by the codefendants. Mandel helped the track obtain extra racing days allocated by the state and worth millions of dollars. The track's secret owners, in exchange, showered the governor with money, gifts and financial assistance in his divorce. The total take, prosecutors said, came to about $350,000.

After losing a lengthy battle to have the convictions overturned, Mandel began serving a three-year sentence at Eglin Air Force Base on May 19, 1980. But under the federal prison provisions, automatically granting inmates days off their sentence for time served in good standing, Mandel will be eligible for release after two years -- on May 31, 1982, according to a Bureau of Prisons spokesman.

The U.S. Parole Commission, considering his case last October, set a parole date of May 14, 1982 -- 17 days before Mandel would otherwise have been released. So far Mandel has earned all the "good time" that if is possible for him to get, the spokesman said.

By setting the parole date, the commission ensured that Mandel would remain under commission supervision, having to report to a parole officer, for one year. Had the commissioners allowed him to complete his sentence on May 31 instead, the supervision would have lasted only six months, a prison spokesman said.

One former Justice Department official, knowledgeable in public corruption cases, said this week, "Mandel simply gets no breaks. My personal view is this case is such a hot potato, the commission is not willing to do anything on his behalf. All discretionary judgements are called against him." But the lawyer added that some legal observers contend that Mandel is just "a prisoner of the parole guidelines."

The commission sets parole dates based on guidelines, taking into account two factors: the inmate's potential for committing future crimes and the severity of the crime he committed.

"The guidelines are set for Mr. Mandel just like [they are] set for numerous other public officials," Malcolm said. "We applied the guidelines no more severely in his case than any others."