MUNICH, West Germany (AP) _ A terrorist bomb planted at the base of a roadside tree demolished an industrialist's passing limousine Wednesday, killing him and his chauffeur and spurting flames 65 feet into the air.

The car carrying Karl Heinz Beckurts, 56, was blown 20 feet off the road near his home, crumpled and riddled with holes. Police found a remote-control cable leading into the woods of the exclusive Strasslach suburb.

A message from the leftist Red Army Faction found nearby said it killed Beckurts, a board member of the giant Siemens electronics company, because Siemens was negotiating a role in the U.S. space defense program known as Star Wars.

The force of the explosion smashed the windshield of a trailing car carrying a bodyguard, who was not injured and described the flames to police.

Terrorists of the Red Army Faction, and its predecessor Baader-Meinhof gang, have been attacking West German industrialists and other corporate, government and NATO targets since the 1960s.

The seven-page letter cited ''secret negotiations for Siemens'' on a possible role in the research program formally called the Strategic Defense Initiative.

Beckurts was a nuclear physicist and head of the Siemens research and development division.

Kurt Rebmann, the chief federal prosecutor, said the reference in the Red Army Faction message was to a preliminary meeting in June 1985 between West German corporate and government officials about the controversial research program.

He said Beckurts' name was on a list of participating business executives police found in a January raid on a suspected Red Army hideout.

Siemens spokesman Werner Osel said the company, based in Munich, has no formal contracts or proposals for participating in Star Wars, which the Soviet Union claims has an offensive rather than defensive purpose.

Police said terrorists hiding in the woods detonated the bomb, which they described as equivalent to 22 pounds of TNT, at 7:30 a.m. as the industrialist's car passed the tree about 800 yards from his home in Strasslach. They said he was on his way to work.

The 42-year-old chauffeur, Eckard Croppler, also was killed.

Bavarian authorities said a cable was found leading from the site of the explosion to nearby woods in the suburb of elegant homes widely spaced in woodland.

Rebmann, the federal prosecutor, denied earlier police reports that Beckurts' BMW limousine was armor-plated.

Officers were scouring the woods hours after the attack and helicopters circled overhead. Authorities said they also were looking for a white Volkswagen van that was believed to be the escape vehicle.

Rebmann showed the seven-page document to reporters at a news conference in Karlsruhe.

It was signed by the Red Army Faction, he said, and included the five- pointed star insignia the group has used in the past.

President Richard von Weizsaecker issued a statement in Bonn calling the murder an ''underhanded crime that is an attack on us all.''

Interior Minster Friedrich Zimmermann described it as ''cowardly, underhanded and brutal,'' and summoned a meeting of ministry security experts.

Johannes Rau, leader of the opposition Social Democrats, said: ''This was not just an attack against a small exalted group of researchers. This was an attack against a part of our entire industry.''

The Red Army letter said the bombing was the work of its Mara Cagol commando unit, named for a member of Italy's Red Brigades terrorist group killed in a shootout with police on June 5, 1975.

Red Army terrorists also claimed responsibility for the last killing of a West German industrialist. Ernst Zimmermann, an executive of a prominent manufacturer of jet engines for the NATO alliance, was shot dead Feb. 1, 1985, in his home only seven miles from Wednesday's bombing.

Federal security officials say about 20 active Red Army faction members remain at large, and estimate they have the support of 200 sympathizers whose identities the authorities do not know.