Leaders of 11 unions representing employes in the automotive component and supply industries said yesterday they are joining forces with the United Auto Workers in an attempt to restrict U.S. car imports.

The announcement by the newly formed Coalition of Auto Component and Supply Workers -- an alliance of unions affiliated with the AFL-CIO's Industrial Union Department -- marks another step in U.S. organized labor's battle to save domestic auto manufacturing jobs it says are being wiped away by foreign competition.

The UAW, claiming its members have lost more than 300,000 jobs largely because of imports, earlier this month filed a petition with the International Trade Commission asking that agency to slap tough import restrictions on foreign cars and trucks. Coalition leaders said yesterday they plan to file a companion petition with the ITC before the end of this week.

"For every assembly worker thrown out of work, at least two workers in auto-related industies lose their jobs," said Elmer Chatak, secretary-treasurer of the IUD and a chief spokesman for the coalition. But, Chatak said, "Little attention has been given to the workers in the automotive component and supply industries, whose plight to date has not been as visible as that of assembly workers."

Chatak claimed that about 650,000 component and supply workers have lost their jobs -- about twice the number of assembly plant employes, most represented by the UAW, who have been laid off.

Overall, an estimated 1 million of the total 1.75 million persons employed in automobile and truck manufacturing and related industries have been laid off during the current economic downturn, he said.

"What we face is not just a temporary condition that will improve as the economy improves. Unlike past periods of high unemployment, the industry's current layoffs may be more prolonged and part of a permanent structural change . . . unless President Carter takes immediate action to curb imports," Chatak said.

Accordingly, Chatak and his coalition members are calling on the White House to impose a five-year quota on auto and truck imports, limiting the number to the 1975-1976 levels of up to 1.7 million units a year.Currently, some 2.4 million foreign cars are coming into the United States and their sales are taking 28.4 percent of the domestic auto market, according to IUD figures.