Just when you thought it was safe to throw away those colored grocery receipts, the hungry jaws of the Washington area's two supermarkets are opening wide again.

Giant Food Inc. and Safeway Stores Inc.'s regional division, both of which are based in Landover, have announced in the past week in radio and newspaper advertisements that they will resume last year's popular computer giveaway promotion this fall.

The programs offer area schools the opportunity to earn free IBM and Apple computers and other peripherals in exchange for store receipts collected.

The promotion was highly popular with Washington-area schoolchildren and their parents, who spent untold hours collecting, counting and bundling the temporarily valuable slips during the last school year.

One Manassas school involved in the Giant effort garnered $1.8 million worth of receipts.

The programs were designed as a public relations effort as well as an educational initiative by the stores, which together take in almost 80 percent of the food dollars spent in the region.

"Computers are such an integral part of most businesses nowadays that students need to be familiar with them when they enter the work force," said Don Gates, senior vice president of Safeway's Eastern Division, which offered its "Computers for Classrooms" program here last year to 1,262 schools in Virginia, Maryland and Washington.

"We hope to surpass last year's record of success," said Giant spokesman Barry Scher of that chain's "Apples for the Students" program.

Last year, Giant gave away more than 7,000 Apple computers, printers and other software packages to 2,300 schools.

Both programs begin Sept. 2 and last until March 1991.