The Treasury Department has found five instances in which substantial quantities of steel have been imported into the United States at prices below the minimum, or trigger prices, the administration put into effect earlier this year to protect the steel industry.

But Treasury sources said yesterday that it is not clear that any of the cases will lead to the first prosecution under the new expedited anti-dumping procedures at the heart of the trigger price system.

None of the five cases involves Japan, the largest steel exporter, sources said.

The trigger prices are based on the costs of production in Japan (plus shipping charges to the United States because Japan is supposed to be the world's most efficient steel producer.

The Treasury set up the trigger prices to prevent what the domestic steel industry charged was wholesale dumping of foreign steel in the American market by foreigners who chose to sell their product at below the cost of production to keep their mills running and their workers employed.

If steel is imported below the trigger price, the Treasury is supposed to begin a quick anti-dumping investigation to see if the steel is being sold below fair value and, if it is, levy special duties.

In an informal statement from the Treasury, the agency said that the Customs Service is investigating the cases.

"The suppliers questioned are claiming that all or most of their shipments either involved a related U.S. importer and have been or will be resold at or above trigger prices . . . or that delivery ws delayed beyond the grace period due to uncontrollable events such as customs brokers' delays," the Treasury said.

"We've had all sorts of stories," one official said, "from claims that icebergs delayed arrival beyond the grace period to a story that a captain jumped ship."

Although Treasury announced the trigger prices on Jan. 9, it provided a grace period for flat-rolled products and rods that were imported under fixed-term contracts. The grace period ended April 30.

Since April 30, the Tresury has experienced few situations in which steel is being imported below the trigger prices. The cases in question arise out of "tens of thousands" of shipments, a top Treasury official said.

In the case of shipments that were delayed beyond the April 30 deadline, it is doubtful the Treasury will find any mitigating factors, sources said.

However, when steel is sold by a foreign manufacturer to a United States company that is related to it (such as a subsidiary), the Treasury must wait until the steel is resold - perhaps even as a finished product - to determine whether the steel was sold below fair market value.

That is common procedure in all anti-dumping investigations that involve the sale of a product by a foreign company to a U.S. subsidiary.

The Treasury will determine whether the steel has been sold below fair market value by substracting from the resale price all the costs the U.S. importer incurred, from storage and handling to actual manufacturing if the steel is resold as a finished or semi-finished product.

Although Treasury sources would confirm that none of the cases under investigation involve Japan, they said that they came from several different areas of the world.