The Turkish consul general in Los Angeles was shot to death today and a group calling itself the Justice Commandos of the Armenian Genocide claimed responsibility for the assassination.

The killing of consul general Kemal Arikan, 54, was quickly denounced by President Reagan as a "vicious act." The president promised federal help for local police attempting to solve the crime, which follows several assassinations of Turkish officials in Europe by Armenians embittered by massacres of Armenians in Turkey 67 years ago.

Los Angeles Police Chief Darryl Gates said, "We have had some belief that he Arikan was in danger. He had been warned." Gates said there had been "a number of threats against Turkish officials . . . security has been tightened considerably in this city." There are between 600,000 and 700,000 Armenians in the United States, with more than 100,000 in the Los Angeles area.

Arikan was shot at about 9:45 a.m. as he sat alone in his car at a stoplight in west Los Angeles. Witnesses said that two young men approached the consul's car, one going to the window on the passenger side of the front seat, the other to the driver's side. Both fired point blank into the car.

Harry Warrington, a maintenance worker at a nearby building, said the shots "sounded like automatic fire. There was so much, so fast."

As the assailants fled into the residential area behind Wilshire Boulevard, Arikan's car drifted across the street, hit a red Volkswagen Rabbit and came to rest against a tree. The driver of the Rabbit, a 29-year-old UCLA student from Korea named Kwang Lim Kim, said that he did not hear the shots. After the crash Kim said he got out of his car and started to walk toward Arikan's car but, "his head was back and I just saw blood and I didn't go there."

Three hours after the shooting Arikan's body was still in the driver's seat, his head slumped back with eyes half opened and a gaping bullet wound in his left cheek.

One police officer said two pistols, thought to be the murder weapons, were found in bushes beside a house two blocks from the scene.

According to Edward K. Bogosian, editor of the Armenian Reporter in New York, Armenian terrorist activities began about 1973. The focal point of their anger is a reported massacre in Turkey in 1915 of more than a million Armenians. Since the early 1970s Armenian groups around the world have demanded that the Turkish government admit responsibility for what they call an act of genocide and make some sort of restitution.

Most of the terrorist activities have been in Europe, where more than 100 incidents have been reported, but today's incident is not the first politically motivated violence against Turks in the United States. In 1973 two Turkish diplomats were shot to death in Santa Barbara, Calif., by an elderly Armenian who was not a member of any organized group. Last November Armenian terrorists claimed responsibility for a bombing at the Turkish consulate here which did extensive damage to the building but caused no injuries.

Bogosian said the Justice Commandos, who called news media in the East Coast to claim responsibility for today's assassination, also reportedly were responsible for the assassination of a Turkish diplomat in Sydney, Australia, last year and for an unsuccessful attempt on the life of the Turkish ambassador to Switzerland. While the targets of the Justice Commandos are most often Turks, they also fight with a rival terrorist group, the Armenian Secret Army. Both groups demand the liberation of Armenia and restitution from the Turks.