The Commerce Department placed restrictions yesterday on the export to the Soviet Union of phosphate rock, concentrates of phosphoric acid and all concentrates of phosphatic fertilizers.

The restrictions would affect mainly Occidental Petroleum Co., which has a $20 billion agreement with the Russians to ship them phosphoric acid used in an Occidental-built ammonia plant. The Russians then ship back to Occidental the ammonia, which can be used in fertilizer.

Before yesterday's action, phosphoric acid was sent under general licenses, which means no prior governmental approval is necessary for shipment. The action yesterday requires that Occidental hold a "validated" license, which means that before the acid can be sent, the transaction must be approved by Commerce.

Commerce Secretary Philip M. Klutznick said he also was suspending new licenses for phosphate exports to the Soviets pending completion of the review of U.S. export control policies which was prompted by the Soviet invasion of Afghanistan.

In a statement released from its Los Angeles office, Occidental officials said that after a review of the situation is completed, "It will be recognized that our fertilizer agreement with the Soviet Union is in the national interest and that halting the export of phosphates to the U.S.S.R. will not hurt them since other countries have additional phosphates available for export.

"In addition, the U.S.S.R. has reserves from its own huge resource of rich phosphate apatite which can be deverted to make up any possible deficiencies," the statement continued.