U.S. exports of steel through the St. Lawrence Seaway - traditionally a tiny portion of Seaway volume - are soaring.

More than 97,000 tons of manufactured iron and steel have traveled to export markets via the Seaway through June. In the first six months of last year, that figure was only 3,000 metric tons."Exports of steel have reached a significant quantity for the first time in a number of years," said David G. Sanders, acting administrator of the Saint Lawrence Seaway Development Corp., which oversees U.S. interests on the waterway.

Mr. Sanders said he expects steel exports to reach 500,000 tons by the end of the shipping season.

"It's the beginning of what we hope is a long-term trend toward steel exports," he said. Mr. Sanders attributed the export rise to the weakness of the U.S. dollar against Asian currencies, particularly the Japanese yen.

Steel is just one component of an export boom through the Seaway.

Overall, more than 3.4 million metric tons of export cargo passed through the Montreal-Lake Ontario section of the Seaway in the first six months of this year - a 131 percent climb from the comparable period of 1994.

Leading the way were U.S. grain exports of 2.4 million tons, a jump of 150 percent from the first six months of 1994.

Mr. Sanders said the increases prove that the Seaway is being viewed as a competitive route for cargo.

"Transportation managers have made a decision to commit or to recommit to using the St. Lawrence Seaway," he said.

Mr. Sanders said that if current trends continue, volume on the Seaway this shipping season will reach its highest level in a decade.