The Puerto Rico Port Authority is continuing its renovation program at the Port of San Juan, as part of its overall plan to attract more cruise lines. In 1984, the Port inaugurated a $3 million pier and passenger terminal, and during 1985/86, it will remodel San Juan's two other passenger terminals.

The port is offering a $1 per head discount off its $4.67 per passenger port charge to any cruise ship that calls in San Juan more than 40 times during the 1985/86 season, and it has frozen its tariffs for one year. In addition, the Ports Authority will soon release a brochure promoting the port, and currently is working on a full-fledged marketing program that it expects to complete within the next two months, according to Luis Dominguez, assistant to the director of the Ports Authority.

According to spokespeople from some of the cruise lines that are currently based in San Juan - Chandris, Costa and Cunard - it is the only Caribbean port that has the facilities to serve as a major gateway. Several travel agents agreed, noting that the port is "well-equipped and handles the flow of cruise passengers smoothly."

The cruise line operators and travel agents also agreed that as a gateway, San Juan is extremely attractive because it enables a ship that is based there to begin its cruise in the Caribbean. As a result, a ship that is based there can visit more ports in a seven-day sailing than one that is based in Florida. It also can sail lower in the Caribbean - a feature that is especially attractive to experienced passengers who want to visit the less-traveled ports. Those interviewed also noted that passengers who sail from San Juan always leave in warm weather, while those who embarked in Florida during the winter risked leaving in colder temperatures.

The only disadvantage cited was the fact that many Florida residents, especially senior citizens, are reluctant to choose San Juan-based cruises because they prefer to drive to the port. However, they also said that the availability of cruise/fly programs is helping to break down this barrier.

While San Juan appears to offer many advantages as a gateway, it is less favorable as a port of call, especially among those who have cruised before, according to the travel agents. Many said that their clients were "a little tired of Puerto Rico," while several others reported that their clients feel the other ports are safer and friendlier.

Nevertheless, more than 460,000 cruise passengers will visit San Juan in 1985/86, and 'thousands more will come in the near future," Dominguez said. Noting that the port can accommodate up to 13 ships at one time, Dominguez said there still is "plenty of room for more ships."

However, one cruise line operator said that currently, there are no more berths available on Saturday, and many of those interviewed expressed concern about how well the city's infrastructure could accommodate additional cruise passengers.

''The ground transportation, baggage facilities and customs areas are not set up to handle a large flow of traffic, so if you suddenly had six, eight or 10 ships calling at one time, there would be a problem immediately," one agent said, expressing the concerns of many.

The biggest concern, however, centers around the airport's ability to absorb the additional traffic. According to those interviewed, there are not enough flights to handle more passengers, nor do they believe that the airport is large enough to accommodate more traffic.

Mr. Dominguez disagrees. According to him, the airport "will not be a problem," and the Ports Authority has no plans to expand it.