OSLO, Norway (AP) _ On the night of Feb. 27, 1943, nine Norwegians quietly slid down a steep, snowy mountain and blew up a German heavy water plant in Telemark, a province in south Norway.

The Allies had ordered the plant destroyed at all costs because it was producing a key atomic weapons element. Joachim Ronneberg, one of the heroes of Telemark, says they succeeded because of ''thorough preparation, excellent intelligence and a good portion of luck. Not in the least the last.

''To pull off a sabotage action like that without even cocking a gun is just unbelievable.''

Ronneberg and eight of his fellow saboteurs, now in their 70s and 80s, are joining 50th anniversary celebrations this weekend. Of the nine men who stole into the plant and the two more who remained behind in the mountains as radio operators, one has died, and another living in Canada did not return for the commemoration.

The ceremonies include a torchlight march to the plant in Rjukan, about 120 miles north of Oslo.

Late Friday, Norwegian military cadets reenacted the attack on the Vemork Plant, now a museum, by sliding down the mountain to the factory. A local church held a memorial service at midnight.

A team of 41 British commandos had been killed trying to land in occupied Norway to attack the Telemark plant. So the Norwegians embarked on what seemed like a suicide mission, which they pulled off without losing a man or firing a shot.

Local residents had fed the Allies information and some of the saboteurs hid for months in the mountains above the plant, while Ronneberg and his five- man team trained in England on a full-scale model of the plant.

Ronneberg's team parachuted into Norway before dawn on Feb. 17. They landed in a storm, 18 miles off target.

''If we hadn't found, by chance, a well-equipped cabin nearby, we probably would not have survived the terrible storm that day,'' said Ronneberg.

After 10 days, they found the local underground team and could begin the mission.

Ronneberg said four men, with machine guns and hand grenades, stood ready to hold off 20 German soldiers. Five found an unguarded path into the building, and fastened explosives to the heavy water equipment or were lookouts. They lit the short fuses, giving them 30 seconds to escape.

As they scrambled up the mountain, Ronneberg said ''we heard a tiny, insignificant pop ... it was almost an anticlimax.''

That pop, just after midnight, destroyed the heavy water equipment.

During their long climb, Ronneberg said the nearly exhausted team kept looking down at cable car that could run up the steep mountain from the plant.

''We were scared to death. If they used the cable car, we were done for,'' he said.

The cable car remained still, and the entire team slipped into the darkness. ''Afterwards, we saw truck after truck with troops going to the plant,'' said Ronneberg.

''Five of us had been ordered to head for Sweden afterwards, it there was any afterwards,'' said Ronneberg.

They eluded a manhunt involving up to 3,000 German troops and skied 250 miles over two weeks to neutral Sweden.

The mission has been the subject of books, and movies, including ''Heroes of Telemark'' a 1950s Hollywood film loosely based on the action.

The saboteurs were awarded medals for bravery by the United States, Britain, France and Norway.

Even their enemy respected them.

''It was the most beautiful coup I had seen,'' said Gen. Nicolaus von Falkenhorst, the commander of the Nazi occupation forces in Norway, after the war.