U.S. marshals here have served papers blocking the departure of three ships loaded with grain purchased by the Iranian government because of fears by the shipper that strife in the Mid-east country will prevent payment of shipping-related charges on those and earlier cargoes.

The Societe Commerciale de Cereales & Financiere S.A., a subsidiary of the giant export firm Louis Dreyfus Corp., has filed five complaints in U.S. district court here seeking seizure of the three shiploads of wheat totaling more than 90,000 metric tons-to secure claims for freight and demurrage charges involving dozens of shipments.

The claims total approximately $10 million and involve the charges due for the shipments for which seizure is sought, for grain aboard three other ships already on the way to Iran and past due charges totaling $4.6 million for grain already delivered. The complaints claim the wheat was purchased by the Iranian government through intermediaries. The wheat on the three ships, which remain tied upin the Portland area, is worth an estimated $12 million.

The Societe, which claims it subchartered the three ships to transport the wheat to Iran, seeks sale of the cargoes to pay its claims.

A source close to the case said the payment of freight and demurrage charges is technically due at the time the cargo is loaded although often not paid until it is offloaded. He said the amounts involved would not have caused any concern except for the disruption in Iran.

The Iranian government, named as one of the defendants in the actions, has not responded, and no date for a hearing has been set.