STOCKHOLM, Sweden (AP) _ A scientist claims to produce nuclear fusion in a jar at room temperature. But few believe him, and his application for a patent is rejected.

The story may sound familiar, but it happened in Sweden in 1927, more than a half-century before two researchers stunned the scientific world with a similar experiment in the United States.

John Tandberg's experiments ''seemingly were very similiar to the ones performed in Utah,'' said Bertil Wilner of the fusion research department at the Royal Institute of Technology.

''It's amazing that his findings have been completely forgotten for 60 years,'' said Wilner, whose father worked on the project and kept notes.

Tandberg began looking into cold fusion in 1927 when the 33-year-old chief scientist for the Electrolux Co. became intrigued with fusion experiments being conducted in Germany, Wilner said.

Two Berlin researchers who were trying to produce helium for airships said they fused hydrogen into helium using a palladium catalyst. But later they discovered errors that forced them to retract their claim of fusion.

''The German scientists weren't interested in producing energy, since the world's energy sources seemed inexhaustable at the time,'' Wilner said.

''But Tandberg immediately realized the energy aspect of the experiment and its potential importance,'' Wilner said in an interview.

The National Patent and Registration Office refused to accept Tandberg's application to record his experiment. ''Their experts claimed it was impossible to release nuclear energy through cold fusion,'' Wilner said.

Soon afterward, Tandberg ended his fusion research and dedicated himself to other fields. He later left Electrolux, still one of the world's largest makers of home appliances, and became a professor at Stockholm University.

In March, B. Stanley Pons, chairman of the University of Utah's chemistry department, and Martin Fleischmann of the University of Southampton, England, announced they achieved cold fusion that produced up to 50 times the amount of energy they put into their experiment.

Their findings were met with incredulity.

The latest scientist seeking to explain away their claims, Nobel laureate Dr. Linus Pauling, suggested chemical reactions, not fusion, could have produced the heat.

Pauling, 88, of the Linus Pauling Institute of Science and Medicine at Palo Alto, Calif., said in a letter published today in the British science magazine Nature that the palladium would have combined with deuterium heavy water to form palladium deuteride, which is unstable.

''After the beginning of electrolysis, this unstable deuteride may begin to decompose either slowly, resulting in an increased liberation of heat, or explosively, as Fleischmann and Pons observed,'' wrote Pauling, who won the Nobel prize for chemistry in 1954.

But, if they are right, it could open the way to a cheap, inexhaustible way to create energy in the same way that the sun and stars produce heat and light. Fusion derives its energy from forcing atoms of deuterium or hydrogen together. The reaction produces an atom of helium, a burst of energy and a neutron.

The work of Pons and Fleischmann ''bears a strong resemblance to the way Tandberg carried out his experiments, according to my father's notes,'' Wilner said. Wilner's father wrote a book on Tandberg describing the experiment.

''The book was never translated and was forgotten a long time ago,'' he said, which helped explain why the work stirred so little interest among contemporary scientists. Tandberg, who died in 1968, apparently never withdrew his claim of having produced cold fusion.

Like Pons and Fleishmann, Tandberg used palladium electrodes placed in deuterium-rich heavy water, Wilner said.

According to the notes, the experiment produced helium and energy. ''But in those days it wasn't possible to record whether the reaction produced more energy than was used to initiate it,'' Wilner said.

There is no evidence that U.S. researchers knew of the experiments in Germany and Sweden.

Johan Rafelski, working on a fusion research team at Brigham Young University in Provo, Utah, was in Sweden last month to report on the U.S. experiments. ''He seemed amazed to find that cold fusion attempts were performed all those years ago,'' Wilner said.