Another Soviet ship reached the Nicaraguan port of Corinto yesterday and several others may be on the way, Pentagon spokesman Michael I. Burch said.
Burch said he did not know whether the ships are carrying weapons.
Other officials said that four or more Soviet or Warsaw Pact ships may be on their way to Nicaragua. Three have passed through the Panama Canal and at least one has rounded South America.
None of the ships is a traditional arms carrier, the officials said, but they are believed to be carrying vehicles, aviation equipment and other cargo with possible military uses.
The Pentagon said that two Soviet ships, the Garri Pollit and the Nova Grudok, passed through the canal Monday and that a third, the Anna Ulyanova, passed through the canal Wednesday.
The officials also said that they now believe Nicaragua may have imported as many as a dozen MI24 Hind helicopter gunships, although not that many have been spotted yet.
Officials previously had said that they believed Nicaragua had received only a few Hinds, which are advanced helicopters that can be equipped with rockets and machine guns.
The Czech L39 jet trainers said to be destined for Nicaragua are still in Bulgaria and have not been shipped to Nicaragua, contrary to some reports, officials said.
But Nicaragua may have received spare parts for the jets, they said.