Container traffic for the trans-Siberian railroad could be shipped from Scandinavia on a ferry service that starts in June between Sweden and Estonia, the Soviet republic on the Baltic Sea.

The new service is attracting so much interest from passengers and Swedish industry that the operators are considering deploying a second vessel.Est Line, a 50-50 joint venture between the Stockholm-based shipping company Nordstrom & Thulin AB and the Estonian Ministry of Transport, will inaugurate the first regular shipping service between Sweden and Estonia for 50 years.

Nordstrom & Thulin has persuaded the Soviet authorities to allow Westerners to enter Estonia without a visa for up to 48 hours, the first time such permission has been granted.

Already, the new line has received 30,000 passenger bookings, according to Ronald Bergman, president of Nordstrom & Thulin. But the real surprise has been the level of interest from industry, indicating a second vessel may be required to meet freight demand.

The strong historical ties between Sweden and Estonia have generated a great deal of business activity between the two sides in recent months, according to Toomas Kabin, the Swedish Trade Council's area manager for Estonia. Most of the major Swedish companies are exploring trade opportunities and the possibility of setting up manufacturing plants in Estonia where labor costs are so much cheaper than in high-cost Sweden.

Joint ventures and other Western investments such as new hotels would require a large volume of raw materials to be shipped to Estonia, and Nordstrom & Thulin is considering whether to acquire another ship.

The new line has already chartered the Dana Regina, a roll-on roll-off ferry, for three services a week between the two cities.

Tallinn could become an important gateway port for the Baltic states and the Soviet Union, Mr. Bergman said. The port already handles grain imports and coal and oil exports and has good facilities, he said. Shippers could save as much as two weeks sending freight by land rather than sea from northern Europe to Asia on an upgraded trans-Siberian railway, Mr. Bergman said last week.