Stanley Cooke lay beached on the sand in front of his $550-a-week oceanside cottage in Rehoboth Beach, Del., his face smeared with oil and his 270-pound frame wrapped in a heavy red quilt.

Although the temperature was nearly 70 at 11 a.m. yesterday, the 15-mph winds chilled the seaside air to a cool 60. But Cooke, a 35-year-old appliance salesman who made reservations for his cottage last January, said he was determined to get a tan anyway.

"Back in June I thought we would never make it, with the gas crisis and all," said Cooke. "But now, when there's gas, it's cold. It feels like October here."

Cooke drove from Hyattsville with his wife Becky and their two children last Saturday to begin their annual two-week vacation in an air-conditioned, two bedroom cottage. But like the thousands of other tourists in town this week, his hopes of long days of body-baking and nights of strolling the boardwalk have been frozen by unseasonably low temperatures.

According to the National Weather Service, the summer of '79 has been an unusually cool one. The average temperature in June was 72 degrees, compared to a 30-year average of 77. In July, the average was 76. Normally, temperatures in that month average around 84.

Though August got off to a sweltering start, the temperature this past week has hovered in the low 70s, disappointing many tourists who have waited all summer for their week or two of seaside vacation.

"The weather is really awful here," said Marianne Loney of Harrisburg, Pa. as she sipped an Irish coffee in a Rehoboth bar Thursday night. The temperature outside was 50, and tourists hurried by, dressed in long pants and sweat shirts. Inside, it wasn't much warmer, and she cupped her glass with two hands for warmth.

"Usually I like to sit on the beach and swim all day. I really love the water. But this week you can just forget that. You come out of the water and you feel like a Popsicle. I've been doing a lot of reading -- inside."

Mort Shapiro, a real estate agent from Baltimore, said he felt cheated.

"Here I am paying $900 a week for a deluxe, four-bedroom house on the beach, and the weather is lousy. I've been cold all week -- do you know how lousy it is when you can't seem to warm up your hands and feet for a whole week?" he said.

"I'd complain to someone if it would do any good, but I don't think the good Lord has a complaint department. When you rent a place in February for a vacation six months later, you're playing the odds. That's why we decided on August. I guess the joke is on me."

Despite the cold snap Adel Vignola, of the Rehoboth Chamber of Commerce, said that just about all of the town's 1,500 hotel and motel rooms were filled by noon yesterday.

"The only thing we have to offer is the sun," said Rehoboth motel owner Charles Steels. "And when people who come here don't get it, they get awful angry. I had one guy earlier this week that threatened to beat me up if I didn't give him his money back. He had paid for a week, but said that since the weather was bad, I should give him his money back. I ended up calling the police. What a nut."

No such problems plagued the tourist business in the Shenandoah National Park yesterday -- vacationers said they traveled there seeking the cool fresh air of the mountains.

"It's totally delicious," said Mary Massimini of Springfield, Pa., "we love it. We brought sweaters. We came prepared."

The Massiminis can retreat to their room in the Big Meadows Lodge when they get cold, but even the campers at the Big Meadows Campground seemed exhilerated.

I love it [camping]. I love the feeling of freedom. Gives me a chance to get away from my paper route. The cold was cold fun," said Matthew Duddy, 12 who is on his 8th annual visit to the campgrounds.

Monday, however, the temperature dipped to 44 degrees. "It was so cold, my father had to heat his key [with a lighter] to start the car," he said.

"We usually sit outside for awhile reading," he said, "but that night we brought the lantern into the tent to keep it warm. Then we got into our pajamas and sweat suits and got into the sleeping bags. I wake up five or six times that night."