Responding to slumping sales and calls from the White House and consumer groups, Ford Motor Co. said yesterday it would immediately guarantee its cars and light trucks against rust perforation for three years.

Ford follows American Motors Corp. in offering the warranty, which has no mileage limitations. AMC's plan does not cover its light trucks, known as Jeeps. Al major U.S. manufacturers have given similar warranties in Canada under a government sponsored voluntary program.

The Ford plan specifically covers all 1980 Ford and Lincoln-Mercury cars and light trucks, and any 1979 model sold on or after July 11.

Ford vice president for North Ameican Operations W.O. Bourke said the warrantly was made possible by recent improvements in "the corrosion resistance we are now building into our 1979 models," including various coating and preserving techniques.

The warranty calls for the free replacement of any auto part which under normal use, develops perforation from corrosion within three years of purchase. Exhaust system components or parts which develop corrosion because of an accident, are not covered.

The Ford action drew immediate praise from the White House and consumer groups.

White House consumer advocate Esther Peterson said she is "delighted" with the action, which her assistant, Ed Cohen, had called for in congressional testimony only two days ago.

"Every once in a while I see a little sunshine at the end of the tunnel," Peterson said. "This is one of those days."

She said she would keep prodding the rest of the auto industry to follow suit, and credited AMC with "opening up the door."

Clarence Ditlow, director of the Center for Auto Safety, also praised the Ford action. "Basically, Ford has finally come around to the side of the consumer," Ditlow said. "For that they should be thanked. I only wonder why it took so long, and why the other major manufacturers have not followed suit."