Sen. Jake Garn, R-Utah, is hopping mad that the Toshiba Corp. of Japan is apparently sidestepping sanctions he pushed through Congress to punish it for shipping advanced technology to the Soviet Union.

Garn held a press conference Wednesday to call on the Reagan administration to immediately enforce the law, saying the administration's delay in implementing regulations is still allowing Toshiba's machine tool affiliate to ship goods to the United States.Garn sponsored an amendment to the omnibus trade bill that was supposed to have placed a three-year imposed import ban on Toshiba Machine Co. for selling advanced milling machinery to the Soviet Union, which Garn said was determined to have seriously damaged Western security.

President Reagan signed the bill on Aug. 23, but implementing regulations for the bill still have not been issued.

Garn said evidence provided by Bob Branand, general counsel to the Society of Plastics Industry, shows 70 Toshiba machines worth millions of dollars are still being shipped to U.S. customers.

"It's too late to stop some of the shipments," Garn said. "But if the administration would move quickly, we could halt some of them. Toshiba apparently is hustling to move equipment into the country before the law is set in concrete with the implementing regulations."

To press the point with the administration, Garn, along with Sens. Alfonse D'Amato, D-N.Y., John Heinz, R-Pa., and William Proxmire, D-Wis., wrote the president complaining that his administration's inaction is allowing Toshiba to break the law.

"Their efforts will be condoned by your administration unless immediate steps are taken to stop it," the letter said.

Garn also said that "even these latest shipments may not end the evasion by Toshiba. Toshiba Machine is advertising the opening of a new sales office in Canada. U.S. industry sources report Toshiba salesmen brazenly suggest that U.S. customers pick up Toshiba machines in Canada rather than risking direct shipment to the United States."

He said, "If this is the case, the parties bringing those goods into the United States will be violating U.S. law and will still be held liable. The laws apply to anyone found bringing Toshiba Machine goods into this country."

Garn said the entire situation is an "outrage." He added, "When they continue to do their level best to get around our laws . . . I begin to question whether the sanctions posed should not be strengthened."