Here is the weather forecast: Dull, cloudy, rain later. Maximum 68 F. Outlook - Changeable.

That is just the sort of forecast that Americans lucky enough to be vacationing in Britain and other parts of Europe are reveling in as the United States swelters from coast to coast. At home they are depending on their air conditioners for survival. In central London today American tourists were wearing coats.

It's not just Britain that has been cool. It has been the same in The Netherlands, Switzerland, Belgium, Sweden and the European section of the Soviet Union, although it has been hot in Greece and Turkey.

Alfred Baumann, mayor of West Paterson, N.J., weighs 350 pounds, and he found the going rough as he packed his bags for England and did last-minute chores in temperatures around 102 F.

"It was hot as bell," said Baumann.

"I noticed the difference as soon as I got off the plane. I felt the cold. It was beautiful. At 5:30 a.m. I woke up it was so cold and put on another blanket to keep warm. That was a real pleasure."

Baumann was leading a party of 57 citizens of West Patterson into Westminster Abbey, and there was not a trace of sweat on his forehead.

The New Jersey group is celebrating Queen Elizabeth's Jubilee with the people of Farmham in Surrey. They are returning the visit a group from Surrey made for the Bicentennial.

Last year Europe had a heat wave - even in places like the highlands of Scotland where such things are unheard of.

A drought emergency was declared and a special minister was appointed to conserve dwindling water reserves in England. For a short time there was even the threat of a massive disruption of British industry.

The hottest summer for more than 200 years was followed by one of the wettest winters, however, and a sort of equilibrium was established.

People who were starting to wonder if they would ever have to go to Spain again to get their summer tan have their answer. British weather has returned again to its predictable unpredictibility.

The other day on the Promenade at Brighton- a leading seaside resorts on the south coast of England - people were happily enjoying the fresh cool breezes off the sea. The English Channel was being left strictly to the seagulls - and a few brave children.

There was frost until the end of May and even a touch of ground frost in central London this month. Glasgow recorded its lowest maximum June day time temperature this century - a shivering 45 F.

"I nearly died in New York. It was 104," said Agnes C. Downey from Bovey, Minn., who was enjoying the cool of the afternoon in Grosvenor Square on the first day of her British vacation. She also stopped at Des Monies and Chicago on the way.

"In Chicago, the hit plane sat on the runway for an hour and we circled around New York for two hours with only token air conditioning. It was terrible," she said.

"It was great when I landed in England. I really loved it - clouds and all. And I don't even care if it rains," said Downey.

Talk to Californians around London and they are blase.

"Sure 106 is nothing for Los Angeles," said one American watching the ducks glide past in St. James Park.But Elyse battistella from Santa Maria, Calif. who was looking through the iron railing of Buckingham Palace at the guardsmen in their bearskin hats feels the drought there deeply.

"It's so depressing. All around you the land is brown and the cattle have nothing to eat."

"The greens in London are so beautiful," she said looking across at the park. I do hope it rains soon. I love the rains.

She need not worry.

She brought two large suitcases with her. One full of warm clothes and the other full of summer clothes. She has not opened the summer case yet.