ATLANTA (AP) _ Coca-Cola, hoping to boldly go where no soft drink has gone before, says NASA violated an agreement by planning to test experimental cans developed by both Coke and Pepsi next week aboard space shuttle Challenger.

The National Aeronautics and Space Administration specified in a written agreement that Coke ''would be the only soft drink tested and consumed'' during the mission, said Coca-Cola Co. spokesman Mark Preisinger. ''As far as we know, we're waiting for clarification on it from NASA.''

''They both probably will be first. Both agreements are virtually identical in what they call for us to do,'' NASA spokesman Charles Redmond said Wednesday in Washington. Redmond said NASA has invited all soft drink manufacturers to develop carbonated beverage containers to be tested aboard shuttle flights.

He said both Coke and Pepsi appear to have begun work on the experiments within ''a reasonable time frame of our initial invitation,'' but that Coke was the first to discuss the project with NASA's food technology laboratory at the Johnson Space Center in Houston.

Including Pepsi would prevent charges of favoritism, he said. ''It gets us out of the bind of having to say that one or the other was first.''

In May, Coca-Cola announced that its special steel can, developed at a cost of more than $250,000, would be carried into orbit this month by the space shuttle. NASA confirmed that announcement last month.

This week, NASA said Pepsi's device, developed by Enviro-Spray Systems of Montgomeryville, Pa., will be on the same flight if final testing under way in Houston is completed in time for liftoff.

Ken Ross, a Pepsi spokesman in New York, said he knew of no pressure by Pepsi to prevent NASA from testing Coke's experimental can alone.

''It's my understanding that NASA welcomed any soft drink company to come up with the technology,'' he said, adding that Pepsi's space can has been in the works for more than a year.

''I have no idea what NASA's arragement with Coca-Cola is,'' Ross said. ''I do know that Pepsi's space can is currently being tested by NASA ... and we are very hopeful that we will be on board the July 12 shuttle with our system.''

NASA has not sent soft drinks into space because conventional containers don't work in the absence of gravity. Astronauts on earlier flights sipped drinks from straws in plastic containers that collapse as they are emptied.