Norfolk Southern Corp. plans to begin a new service in early 1984 that will allow giant coal-carrying ships to be loaded to full capacity instead of leaving Norfolk ports only partially loaded because of the limited depth of the port's channel.

The company said yesterday it will provide a "top-off service" by loading more coal onto the ships from barges anchored in deeper waters in the lower Delaware Bay.

The plan is designed to help increase coal exports. "We expect this operation to lower significantly the per-ton cost of coal moved overseas and result in larger coal sales for U.S. producers," said Robert B. Claytor,Norfolk Southern chairman.

Rep. Rick Boucher (D-Va.) said yesterday that in 1982, U.S. coal producers lost sales valued at nearly $26 million because no topping-off service was available from Norfolk's Hampton Roads shipping area. Instead, some of those ships topped off loads of U.S. coal with coal picked up in South Africa, he said.

Coal ships bigger than 100,000-ton deadweight capacity cannot be fully loaded at Norfolk because of the 45-foot channel depth thet Coast ports have channels even more shallow.

With the new service, colliers partially loaded at the Norfoilway's Lamberts Point coal pier would proceed to coal-loaded barges anchored at Big Stone Anchorage in the lower Delaware Bay, where the depth is 55 feet.

The company has agreed to buy a 35,000-ton self-discharging bit will also lease a 21,000-ton barge and a tugboat for the service. The anchorage in the Delaware Bay can accls of 150,000 tons or more. Even in waves as high as 10 feet it should be possible to transfer coal from the barge to a coal ship, the company said.

Norfolk Southern ated its second-quarter results yesterday. The company earned $74.9 million ($1.19 per share) in the second qua83, down substantially from $138.2 million ($2.21) in the same period in 1982. Revenues were $799.1 million compared with $916.9 million. Reduced coal shipments were a factor in depressing the company's earnings this year.