Vice President Bush yesterday rejected his predecessor's criticisms of the Reagan administration foreign policy, saying a critical speech Tuesday by former vice president Mondale was so overstated that "I thought someone had put LSD in my coffee."

Responding in a speech to an export trade group at the Capitol Hill Club, Bush said that Mondale was the last person to be making such an attack on the new administration.

When he saw that Mondale had said that Reagan had "sown doubt and confusion" among the European allies, Bush said he asked, "Could this be the same Fritz Mondale who helped shape the policies of an administration under which our European allies were informed that we were going to deploy the neutron bomb and then were told we weren't?"

When Mondale charged that the United States' "failed economic policies are biting our industrial state partners," Bush said he wondered, "Could this be the same Fritz Mondale who helped shape the policies of an administration under which the inflation rate went from 4.6 percent to 12.4 percent, the growth rate went from 4.7 percent to minus 1.3 percent, and the prime interest rate went from 6.4 percent to 20.4 percent?"

"After thinking it over," Bush said, "I decided that it couldn't possibly be the same Fritz Mondale. It must be some impostor. But I do think the real Fritz Mondale should tell this other fellow to stop, before he gives him a bad name."