A strike by truck drivers that began earlier this month is paralyzing port activity and movement of cargo in Panama's Colon Free Zone, executives said.

''We're open. Everyone's working, but no cargo is moving,'' said Eugenio Ruis, chief of transport in the free-trade zone as truckers started a 72-hour strike Wednesday.A 48-hour strike last week by truckers in Colon caused millions of dollars in lost business for Colon Free Zone companies and the four recently privatized ports on the Atlantic and Pacific entrances to the Panama Canal. Those companies rely heavily on trucking to move cargo arriving from all over the world.

Though Mr. Ruis said the drivers ''are not blocking anything,'' the strike is ''paralyzing their (CFZ users) operations.''

The Chriqui Truckers Union is protesting a free-transport agreement signed by Central American countries and Panama in January, which allows free shipment of cargo through the region, smashing the hold of Panamanian truck monopolies established in the 1970s.

Panamanian truck drivers believe the agreement is unfair, union officials say, because a truck from elsewhere in Central America pays just $4 to bring cargo into Panama, but a Panamanian truck pays up to $800 to take cargo into Central America.

Analysts have said the situation reflects some of Panama's growing pains as it leaves behind centuries of protectionism and uneasily ushers in a new era of free competition.

Unions in the frontier province of Chiriqui have been striking since March 4, and the strikes appear poised to continue.

''We have not lowered our guard,'' said Carlos Alvarado, leader of the Chiriqui Truckers Union.

The government has said it cannot rescind the agreement, known as Resolution 64-98 - noting it took extensive negotiations with other Central American states. The agreement spells out terms and conditions for free contracting of transport services between Central American countries.

Meanwhile, John Bressi, general manager of Manzanillo International Terminals - which operates the main terminal for Colon Free Zone exports on the Atlantic Coast - said, ''There was no cargo leaving the terminal'' by road during last week's strike.

But while the strike has hurt companies in the zone, the terminal operator itself has been affected only slightly.

''All of our operations are continuing as normal,'' Mr. Bressi said, noting that the strike is causing a slight backlog of containers.

Truckers stopped their strike last Sunday after Ricardo Saval, governor of the northeastern Chiriqui province, said the resolution had been suspended. But the strikes resumed when it became clear that Mr. Saval's statement was not in line with that of the government in Panama City.

Mr. Bressi said the protests were peaceful and that cargo was permitted to arrive and depart the port. But analysts say the strikes could turn violent if trucking companies from Panama attempt to break the strike.