The Secret Service wants movie makers to return fake money that looks so genuine some people are spending it. Bills with face values totaling about $1 billion were blown up in recent filming of the action movie ''Rush Hour 2'' in Las Vegas. Some of the bills fluttered into the hands of people who later spent them, the authorities said. The Secret Service ordered Independent Studio Services Inc. of Sun Valley, Calif., to stop making the fake money and sent a recall letter to every production company that ordered the prop cash.