December is when Ocean City is out of order. The 700-room Sheraton-Fontainebleau has exactly nine cars in the parking lot on a Friday afternoon. The Morbid Manor fun house on the boardwalk is so tightly shuttered that it looks morbid.A sign at a carryout loudly advertises "Philly-Style Hoagies!" -- but the "Closed" sign directly beneath it tells the real tale.

So it was surprising, 12 days' before Christmas, to find Harry Kelley plotting, promising, boasting and bellowing as if it were July 4.

Kelley, 61, has been mayor of this 81-year-old Atlantic beach community for nine years.He likes to think of himself not just as the guy who fixes potholes, but as Ocean City's chief promoter and image-preserver. In addition, he just might be the most boisterous and buoyant mayor ever to hand out a key to his city.

Put it all together, and you get a Kelly pep talk that goes like this:

"I'm here to tell you, you betcha, listen to what I tell you: We are going to have our greatest year ever in 1980. Yes, sir! The greatest! Family vacations are bigger than ever!"

But so are Ocean City's problems.

Despite last summer's gasoline melodrama, which "played" well into the usually booming month of July, hotel occupancy in "The White Marlin Capital of the World" was up 13 percent over 1978 totals, according to the Ocean City Chamber of Commerce.

The human crunch was even greater.

"It's simple," said John Rolfe, an Ocean City real estate broker for 20 years. "We get 200,000 people a day here in the summer, and they seem to drive 300,000 cars."

The result is familiar to any urbanite: unrelenting traffic jams on Ocean Highway, the main street -- some lasting past midnight.

According to one Ocean City businessman, it was "nothing last summer for it to take me five minutes to drive five blocks," even though Ocean Highway is six lanes wide.

So Kelley is moving in two ways to limit the human surge of summer. He is "fighting to keep gambling and the gambling people out" -- and so far, he has been successful. Meanwhile, for the first time, he and the City Council are considering putting a limit on the number of cars allowed to enter the city.

Town leaders adamantly oppose gambling, but that is because of the prostitution and crime it would probably bring, not because their resort town has always been pure in that respect.

As recently as the 1950s, according to William Purnell Sr., owner of the Atlantic Hotel at Wicomico Street and the boardwalk, slot machines were common in Ocean City hotels.

"They weren't illegal; they were just frowned upon," Purnell said. And depending on who you knew, "you could find a horse book, a poker game, just about anything."

But Ocean City officials point to Atlantic City's experience as evidence that gambling in a resort town of the late 1970s is a two-sided coin.

"How much family business are they doing?" asks Kelley, of his New Jersey neighbor. "Other than six blocks, gambling is a big zero there.

"We got the ice cream and cake here already, for lots of Ocean City people. We want to be a family resort for everyone from the $25-a-day guy to the $100-a-day guy. And we are."

Still, almost everyone drives to Ocean City, and that means almost everyone must find a place to park. In the summer, that can be close to impossible.

The only municipal lot, at the southern tip of town, contains about 1,000 spaces. According to several local residents, it was routine last summer for drivers to spend four hours cruising the lot before finding a space. Kelley delights in pointing out that more cars ran out of gas circling the lot than in getting to or from Washington or Baltimore.

Among the traffic-reducing proposals city officials are studying are:

Building a satellite parking lot in West Ocean City, across Sinepuxent Bay, and providing shuttle bus service.

Doubling the size of the municipal bus fleet, and reducing or revoking the present 40-cent fare to encourage people to ride buses.

Banning single-occupant cars from entering the city.

Adding to the fleet of "caterpillars" that shuttle up and down the boardwalk, and doing away with the 25-cent fare they now charge.

Neither Kelley nor other city officials will predict which measure, if any, is most likely to be enacted.

"All we're saying is that it's time to think about this," Kelley said.

It is also time to think about gasoline again.

Kelley became world-famous last summer (CBS Evening News, New York Times, Der Speigel) when, without City Council permission, he spent about $80,000 in city funds to stockpile gasoline in Ocean City.

The idea was that the gas would be a hedge against economic disaster -- a guarantee, as Kelley put it at the time, that "if you get here, we'll get you home."

What made Kelley look like a genius was his timing. He bought most of his gas in April, two months before the lines and shortages. Thus, his resort was the only one in the east -- and one of the few in the country -- to show a double-digit percentage gain over the previous summer's gross.

In fact, what Kelley calls the "ultimate ego trip" arrived by telephone the other day.

A slick Los Angeles consulting firm, hired by the city of Las Vegas, called to ask Kelley's advice. How could the Nevada resort buy some gasoline for itself?"

"I had trouble passing the third grade, so I kind of liked that," said Kelley, with a belly laugh.

What about gas and Ocean City, 1980?

"I ain't saying about this summer, because I can't yet," Kelley said. "And I'm not sure I have to do anything just yet. I've still got about 100,000 gallons from last summer left over."

The gas is stashed in tanks all over Ocean City, Kelley adds, "at locations I can't discuss."

Also stashed about town are 3,560 year-round residents -- mean age 43, mean family income $12,000 a year, mean length of residence in Ocean City about 35 years.

"It boils down to a group of people who have been here all their lives," says Bill Esham Jr., a 36-year-old furniture dealer, who says he remembers Kelley bouncing him on his knee when Esham was a baby.

The year-rounders are extremely conservative politically. They gave archconservative Republican U.S. Rep. Bob Bauman one of his largest victory margins in 1978.

City folks would find year-rounders socially square, too. They like square-dancing at the volunteer firehouse. They go hunting and fishing, but seldom discoing. Ask them to point with pride at a civic accomplishment, and they are likely to note that the local McDonald's set a record on May 29, 1977 -- most breakfasts served in one day (4,689) by any McDonald's anywhere.

As for menaces, many year-rounders say the worst they face is "dirtballs" -- the local name for the backpacking, penniless young people who arrive in droves every summer.

"Sometimes I just want to tell them to take a bath," said Sarah Lynch Purnell, William's wife.

But no one has to tell them to spend money.

"We have the Atlantic Ocean and one of the finest beaches in the world," said Esham. "I'd like to work on the overcrowding, but overcrowning alone won't keep anyone away. If they have to stand in line for a hamburger on the boardwalk for a few minutes, I think they'll live."

Or as Harry Kelley puts it: "We got a nice thing going here. Real sweet. Real nice. We want it to continue."