With a wave over his soulder and a tight-lipped smile on his face, Marvin Mandel lugged a heavy suitcase down a long, palm-lined sidewalk this morning and began the prison term he fought for nearly three years to avoid.

The humiliating walk ended for the moment the highly visible public career of a man whose ability to "work it out" catapulted him from a Baltimore law practice to two terms as Maryland's chief executive.

The diminutive former governor, wearing a light summer suit and sunglasses, displayed the same lack of emotion he exhibited in August 1977 in the federal courthouse in Baltimore when a jury found him guilty of a scheme designed to enrich him and five of his friends.

Mandel arrived at the minimum security prison a few minutes before 7 a.m. in a dark green rented Pontiac driven by his wife, Jeanne.

They kissed quickly and then Mandel strode briskly toward the camp's administration building, lumbering under the weight of his heavy suitcase.

After completing the initial processing, Mandel took his place among the prison's 365 other inmates, who include two of his friends and codefendants, Irvin Kovens and Harry W. Rodgers, who began their three-year sentences Thursday.

Mandel was originally scheduled to begin his own three-year sentence the same day, but U.S. District Judge Robert Taylor allowed him to postpone his arrival at Elgin until today for personal reasons. a

Whether Mandel will get to be in the same dormitory with Kovens, his lifelong friend and political mentor, will depend on the luck of the draw. Prisoners are divided into four groups by order of their admission, and assistant superintendent Dave Swyhart said he didn't know whether Mandel had been placed with Kovens.

As first offenders, Mandel and three codefendants who also went to prison technically are eligible for parole immediately. But as a practical matter, according to a spokesman for the Federal Bureau of Prisons, inmates normally serve at least four months.

The average sentence of men assigned to Eglin is three years, the same as Mandel's, and the average stay is 13 months, which was the time served here by another famous felon, Watergate figure E. Howard Hunt.

Mandel began his prison life in a brown-and-white wooden dormitory which was remodeled by inmates from a World War II military barracks. He was assigned a bunk bed, metal locker and towel rack in a stuffy open room, cooled by a large fan, with 28 beds.

Some time in the next three to six weeks, after he learns how to make his bed and master prison regulations, Mandel will graduate to one of four new carpeted and air-conditioned dormitories that offer privacy cubicles where each inmate has a bunk and a built-in cabinet and bookcase.

Assistant superintendent Swyhart, who spent four and one half of his 12 years as a prison administrator at Leavenworth, said the major differences between so-called "country club" prisons such as eglin and maximum security institutions such as Leavenworth as "the height of the walls and the control of movement inside." He said the recreational facilities and visiting privileges permitted behind the 40-foot walls at Leavenworth are about the same as on the campus setting here in the Florida Panhandle.

"This place benefits the taxpayers," said Swyhart, noting that the national average for maintaining a federal prisoner is $27 a day, compared to $14 at Eglin.

Another misconception about Eglin, according to Swyhart, is that it is an exclusive haven for white-collar prisoners. Not so, said the superintendent. More than half of the inmates were convicted of drug offenses, many of them young men caught importing marijuana.

About 15 percent of the prison population committed white-collar crimes and only a handful of those, like Mandel, are lawyers.

While two-thirds of the inmates here are, like Mandel, white (20 percent are Hispanic and 12 percent black), only a dozen are older than 60-year-old Mandel and fewer than that older than Kovens, who is 61. The average age of the inmates is 32.

Mandel will be able to keep in touch with his friends by making unlimited collect telephone calls from any of the 14 phone boots scattered about the camp. He also can write uncensored letters as long as he buys his own stamps. And he can subscribe to home-town newspapers and receive money to supplement the $5 to $25 a month he will earn for performing whatever task -- likely mowing lawns on the huge air base -- to which he is assigned.

Prisoners may spend up to $75 a month at the camp commissary, where the pipe-smoking Mandel will be able to choose among four brands of pipe tobacco. And if he doesn't find his favorite brand on the shelf, he can order it.

The prices in the commissary are so low that a woman employe of the prison said, "I get mad every time I go to the supermarket."

In addition to tobacco, prisoners can buy slippers, sunglasses, coffee mugs, shaving equipment, ice tea, cookies, pickles and peanuts. Among the best selling items are tennis balls and racquets -- the four outdoor courts are so popular there often is a waiting time.

Throughout two trials -- the first one disrupted by reports of jury tampering -- and three appeals, Mandel maintained, if not innocence, a contention that "I never during the tenure of my office ever defrauded the people of Maryland of anything."

And many of them still believe him. Before he flew to Florida over the weekend, Mandel stopped in Chick and Ruth's Deli in Annapolis on Saturday and presided for the last time in a while -- at a booth that is labeled "The Governor's Office."

As the ex-governor munched a cream cheese-filled bagel, owner Chick Levitt praised Mandel as "a great governor, one of my favorite people," and vowed never to remove from the menu sandwich number 16, The Governor Mandel, (chopped liver and corned beef).

The sandwich named in honor of Mandel's predecessor, Spiro T. Agnew, was removed from the menu after Agnew was forced out of the vice presidency in disgrace.