Marvin Mandel said he "felt a little ridiculous." There he was, the A former governor of Maryland, walking into the state board of elections office here to register to vote.

Maryland's 56th governor lost his voting rights when he became a convicted felon. With his release from prison in December, the only way Mandel could get his name back on the Maryland rolls was to trek to the elections board office and put it there. So he did.

It was one of many things Mandel had to do to start over, and he is doing them almost daily. Step by step, he is wading back into public life, sometimes feeling ridiculous about it, sometimes relishing it. He is not yet exerting political influence--at least not overtly--but he is certainly making his presence felt.

"It's a little sad to watch," said an old Mandel friend. "But you've got to admire the fact that he's not going to roll over and play dead."

In the last two weeks, Mandel has become a Monday night regular at a popular Annapolis watering hole where lobbyists, legislators and political gossips trade information. Lately, he has been honored at welcome-back-Marvin luncheons, like the one at the Capital Center last month that was hosted by a dozen influential Prince George's County politicians and businessmen. Each guest chipped in $100 to buy a gift for the man they still call "the governor"--a painting of Mandel's old Annapolis haunt, Chick and Ruth's Delly.

"It was just a friendly gesture to let the governor know we're glad he's back with us," one of the guests said. "He said he wanted to thank us for all we'd done on his behalf, some of us more than others."

Mandel and his wife Jeanne insist that there is nothing notable about these recent coming-outs. He is just private citizen Marvin Mandel, they say, going about his life in this fishbowl of a town. "I'm too busy trying to reorganize my life to be anything else," he said.

But it isn't quite that simple. Last week, the private Marvin and Jeanne Mandel traded a little on their public names, placing an advertisement in local newspapers with this eye-catching headline in bold type: "Attention prospective investors: Jeanne & Marvin Mandel. . . ."

The small print went on to say the Mandels "cordially invite" the public to a seminar on how to cash in on the Reagan tax laws through real estate investment--a subject on which Mandel is known to have little expertise. The seminar was being held "in cooperation with" Norris Properties of Washington, D.C., the ad explained.

As it turned out, Norris Properties, owned by Norris Ashe, is one of many clients of the Mandels' public relations consulting firm, founded by the couple after the former governor's 1977 mail fraud and racketeering conviction. Jeanne Mandel is on the Norris Properties payroll as a consultant, Ashe said, and Marvin Mandel, he noted, is "one of my financial advisers. I've known the governor personally for many years."

Ashe said the seminar was intended to drum up business for his firm, which sells and manages real estate properties. The Jeanne & Marvin ad certainly helped his prospects. It drew 62 men and women, many of whom said they came either because they expected to see and hear the former governor, or because the Mandel name in the ad caught their attention.

But Mandel was hardly the featured speaker. After greeting guests at the door to the magenta-carpeted meeting room at the Annapolis Hilton, he took his place in the audience and sat silently, puffing on his trademark pipe. Jeanne Mandel provided only the introduction: "Marvin and I would like to welcome you and hope you have an enlightening, educational and profitable evening."

From then on it was Ashe's show. Rosy-cheeked and barrel-chested, Ashe buoyantly led his audience on a tour through the wonderful world of tax shelters, depreciation and interest write-offs through real estate investment--a tour clearly intended for the uninitiated.

There were such nuggets as: "It is not unpatriotic to not pay taxes because the president has said he'd rather you didn't pay taxes and put the money in the economy." Ashe also introduced his listeners to the three kinds of properties in the area, using posters with the headings "Suburbs," "Baltimore," and "Washington." In closing, he urged his audience to strike while the market is tight, since sellers tend to make more concessions than usual. "I love it when it's like this," Ashe said. "You can make deals like you could never make in old times."

All of this was very interesting, several members of the audience said, but not what they came expecting to hear.

"So far I feel like I've missed a good night of TV," said Joe Rogers, a retired government employe who drove 35 miles from his home in Adelphi to attend the seminar. "It sounds like a long commercial for Norris Properties to me. That ad about the Mandels was just a big lure."

Marvin and Jeanne Mandel expressed irritation at the suggestion that they had let their names be used. "No one was using me," Mandel said, still puffing on his pipe. "Jeanne and I are conducting this seminar in conjunction with Norris Properties. That's what the ad said. We hoped people would turn out."

"We're just people," Jeanne Mandel said. "I wish people would realize that. We're in business. We're working people just like everyone else."