When American ships began sailing for China from Baltimore's port soon after the War of 1812, trade consisted mostly of silver and opium in exchange for Chinese silks and tea.

Since then trade has changed somewhat.

For example, Americans no longer use opium for barter -- at least not legally -- and the Chinese have expanded their exports beyond silk and tea, although that expansion has been limited.

Now the Chinese are attempting to move full steam ahead in the international flow of trade, particularly by buying heavy machinery, industrial equipment and, in some cases, whole plants from the United States, its newfound trading partner.

And waiting to serve this new trade with the Peoples Republic of China is a newer version of the 274-year-old Baltimore port that welcomed them in the early 1800s, was home to the Baltimore clipper ships and withstood near devastation during the War of 1812, the Civil War and the Great Fire of 1904.

With the recent opening of trade with China and the granting of most-favored-nation status to the Chinese, Baltimore port officials are expecting a swell of business -- mostly in exports -- that is sure to enhance what Gov. Harry Hughes has called "the single most important economic asset of the State of Maryland": its port. It also alternates between the third and fourth largest port in the nation.

"China doesn't want to import finished products -- our textiles, shoes," said Don Klein of the Maryland Port Administration. "They want heavy equipment so they can make their own. They want to build plants. They want to go through this period of industrializing their society."

Three key areas the Chinese are interested in are engineering, mining and shipbuilding, Klein said. In fact, the Chinese merchant marine fleet is so small that it probably will have to rely on vessels from the United States and other countries to deliver the goods it buys, Klein added.

A lot of China's imports will leave this country through Baltimore because of its proximity to the Midwest where most of the heavy machinery the Chinese would import is made, Klein said. The port has been the host for Chinese representatives on at least eight occasions recently to underscore the port's good points.

For example, Baltimore is 123 miles closer by train to Chicago than New York's ports are, and 143 miles closer by truck, according to Maryland Port Administration figures. It is located 12 miles northwest of the Chesapeake Bay, the country's largest estuary, and it is the only port that can be approached from the ocean by two distinct routes: from the south by way of Cape Charles and Cape Henry and from the north by the Chesapeake and Delaware Canal.

"We went through the exact same thing with the Middle East oil-rich countries," Klein said. When they increased their trading with the United States, a large part of their business went through Baltimore, particularly exports of industrial plants and aircraft and imports of petroleum products. The port exports more heavy manufacturing cargo to the Middle East than any other U.S. port.

The port here also had a large hand in shipping equipment overseas during the Vietnam war, Klein said, and before the reign of Ayatollah Ruhollah Khomeini it handled a large part of military cargo sent to Iran. It also helped deliver most of Russia's Kama River truck plant before the U.S. government froze shipments of high-technology and other equipment there in response to the Soviets' invasion of Afghanistan.

Klein said port officials don't know when this expanded China trade will begin or how much it will be. But they already are planning to get a large chunk of it and have instructed their trade representative in Hong Kong to try to steer a lot of the business here.

Trade with China through Baltimore has practically nowhere to go but up. Chinese exports and imports totaled only 26,000 tons for the first nine months last year while for the same time trade with the Middle East through the port amounted to 3.4 million tons. North Europe, including the United Kingdom, Germany, France and the Scandinavian countries, comprised 5.3 million tons of the port's annual 60 million tons of foreign and domestic business.

U.S. exports to China through Baltimore consisted mostly of cast-iron pipes and tubes, aluminum plating, iron and steel plates, special industrial machinery, boats and small shipments of X-Ray equipment, chemicals and machine tools, Klein said.

On the other hand, imports passing through Baltimore from China included base metals, cotton and silk handkerchiefs and other apparel, porcelain and china, bauxite and beer, ale and stout.

In contrast, the Virginia ports probably won't see much more business with the Chinese because vessels of Communist countries haven't been allowed there or at ports in San Diego and Charleston, S.C., form many years because they are near major military installations, according to Priscilla Graybeal of the Virginia Port Authority.

During the first six months of 1979, U.S. exports to China through Virginia ports amounted to 39,408 tons of goods valued at $11.2 million, Graybeal said. Those exports were almost exclusively corn and soybean oil, she added. During the same period, the United States imported through Virginia 964 tons of goods worth $1.5 million which consisted of tea, resins, carpets and rugs, shellfish, rattan materials, chemicals and materials of animal origin.

That business had grown tremendously, however, from the same period in 1978 in which exports to China through Virginia ports were valued at $137,513 and imports from China were worth $1.4 million, Graybeal said.

In handling merchandise that's packaged, boxed or crated as opposed to poured on board, such as grain of oil, Baltimore's port, once considered a worthless mud flat, ranks second on the East Coast behind New York, Klein said. Baltimore also specializes in project shipping in which an entire plant may be sent overseas. For example, recently a power plant was shipped to Turkey through the port here, Klein said.

The Harbor here takes up 45 miles of waterfront and is surrounded by nearly 1,600 acres of sheltered waters. It uses 99 covered and open piers for loading and unloading of about 200 vessels at one time. The port is also equipped with a crane that can lift 350 tons at one time and therefore will be valuable in hoisting large pieces of machinery the chinese might want, Klein said.

Each year the total impact of the port on the state's economy is more than $3 billion, or about 10 percent of the gross state product. It is also the source of more than 170,000 jobs, one of every 10 in the state, according to a University of Maryland study.