Loud as it was, the whirring of the "Big Six" roulette wheel was nearly drowned out by the clatter of plates. Four harried caterers were trying to keep the buffet tables filled with enough roast beef, potato salad and cole slaw to keep Marjorie Holt's supporters from going hungry.

The Bay Ridge Inn, where silverdollar slot machines had once drawn crowds of the curious until they were outlawed in 1968, this afternoon played host to about 1,400 of Holt's supporters who had arrived for her annual "Bull Roast" fundraising picnic.

They came for a few pieces of the beef roasts that were blackening slowly on open grills; they came to exchange pleasantries with the Republican congresswoman from Maryland's Fourth District; and they came to hear Gen. Alexander Haig, the former supreme commander of NATO, tell them their country was adrift and needed to get back on course.

Holt's Bull Roast, the annual September outing for Republicans from Anne Arundel and Prince George's counties, is a monument to a political truism; that for a congressman, an election is never far away.

It has been less than a year since Holt won her fourth term in Congress and it is more than a year until her next contest. But Holt's campaign committee, which has never been disbanded since she first won office in 1972, has also never stopped fundraising.

Mike Owen, an aide in Holt's congressional office who helped organize the gathering, estimated that more than 1,650 $15 tickets were sold this year to everyone from the head of the state's powerful medical lobby to longtime precinct workers, and from former superintendents of the Naval Academy to Anne Arundel county executive Robert Pascal. Owen said he expected the Holt campaign would net about $12,500 from the affair.

"It's in the nature of the job," Owen said, as he watched one picnicker after another go up and touch Holt's arm and offer a quick compliment. "If the congressman's doing a good job, he is campaigning constantly -- 365 days a year."

Holt herself put it differently. Her campaign committee, The Friends of Marjorie Holt, is "a sustaining club," she said, constantly picking up funds to pay for the growing cost of her campaign. (The 1978 effort alone cost about $100,000, Owen said.)

"This way, you don't have to have frantic spurt campaigning," Holt said. "It's just steady, constant work, and it keeps people aware that you're in office," she said.

The people who came to Bay Ridge Beach along the Chesapeake Bay today were well aware of the conservative Republican congresswoman's role on Capitol Hill; many of them had worked with her and supported her from her earliest days as a member of the local PTA.

"She babysat for some of these people when she was with the PTA," said Owens.

While keeping herself and her work fresh in the minds of her own constituents, Holt has also been able to draw Republicans of national stature of her gatherings. Sen. Charles McC.Mathias stopped by today. Last year, the featured speaker was presidential hopeful George Bush.

And this year, that role was filled by Haig, who called for new national leadership, but remained coy about his own possible condidacy in the 1980 presidential election.

"The days of our involvement with Southeast Asia are over," Haig said. "But the days of the paralyzing, mesmerizing, sackcloth-and-ashes attitude that dominates American leadership must also be over."

Haig received a warm reception from the group, and was stopped after his speech by several people who urged him to run for the White House.

But while Haig's brief appearance caused a stir among some of those at the gathering, Holt remained the center of attention. One after another, constituents would come up to her as she walked through the picnic tables asking for help with this problem or reminding her that they met her at some other gathering during some other campaign.

"Oh, yes," she said again and again. "I remember you." Or, "just call my office, we will be able to help you, I'm sure."