Rio de Janeiro could eventually surpass congested, overpriced Santos as Brazil's main coffee-exporting port, thanks to an $83 million investment by local entity Multiportos Operadora Portuaria S/A.

The company - a subsidiary of the Multiterminais holding group - is now leasing the installations of Brazil's formerly insolvent Industrias Verolme Ishibras alongside the Rio-Niteroi bridge and Rio's Tecon container terminal.''Because it is a private terminal located outside the premises of the port,'' says the U.S. Commercial Service, ''the Multiportos terminal will be able to directly hire its work force contingent, unhindered by the constraints of Brazil's port labor legislation, and thereby avoid very high Brazilian stevedoring costs and rigid work rules.''

That will lower the labor cost - currently $400 per container, among the highest in the world, to $60 per container, industry observers predict. Multiportos plans to invest $83 million in its planned coffee terminal, with $43 million of that to be spent on equipment, $24.4 million on pier upgrading, $9.5 million on dredging and $6 million on miscellaneous installations.

Etienne Kvassay, a port specialist at the U.S. Commercial Service office in Rio de Janeiro, said that because the Multiportos terminal is not located on the port premises, ''union costs, work schedules and contracts will not apply. They can freely contract labor without any consideration from unions. That is the difference.''

He adds that the new terminal is expected to handle 3,500 coffee containers this year, or 15 percent of Brazil's total coffee exports - giving Rio a bigger share of the business than ever before.

In 1996, according to statistics provided by the Federation of Brazilian Coffee Exporters (Febec), Santos handled 62.6 percent of Brazil's coffee exports, followed by Vitoria (28.6 percent), Rio de Janeiro (5.8 percent) and Paranagua (1.7 percent). The importance of coffee to the Brazilian economy cannot be overestimated. In 1997, total green coffee exports came to $2.73 billion, a 61 percent jump over 1996 figures.

Brazil ranks as the world's largest coffee exporter, with more than twice as much land under cultivation as the world's No. 2 producer, Colombia.

At the moment, Brazil's largest coffee exporter, Unicafe, is predicting that the country's 1998-'99 crop will total 35.2 million bags - substantially more than the 31.2 million bags estimated by the Ministry of Trade in late January. The projections by Unicafe, which accounts for 10 percent of Brazil's coffee exports, are similar to those made by Febec, which thinks the 1997-'98 harvest came to 23 million bags, and that the 1998-'99 crop will reach 33 million bags. Each bag holds 132 pounds.

Febec adds that about 600,000 bags of robusta coffee will reach the market in April and May 1998, and that during June, about 1.5 million bags of both robusta and arabica will be available.

Yet Brazil's unusually high port costs eat away at profits - something coffee exporters complain about constantly.

''We are hoping that privatization of the railroad system and the building of new ports will help us,'' said Febec President Oswaldo Aranho Neto. ''The port structure in Brazil is still extremely expensive. Febec was part of the movement by several business associations to change regulations to enable the ports to become more efficient. We have too many problems with theft, and we want to avoid that.''

Rio-based Multiterminais owns a 10 percent stake in a consortium that paid $250 million last September for a 25-year concession to operate the main container terminal at Santos. Hamburg port operator HHLA is advising the consortium on how to reduce handling costs from $500 per container to $150 within the next two years.

According to Mr. Kvassay, ''Multiterminais is leasing the installations of IVI, which was almost bankrupt. It was the largest shipyard in Brazil, but was in very bad financial straits. It was unable to keep its contract with Petrobras and other contracts, and for this reason, it technically ceased existing, and Multiterminais took over the lease.''

Unfortunately, both ports are routinely plagued by strikes - a contrast with the southern port of Rio Grande. In early February, after becoming the first Brazilian port to be privatized, Rio Grande officials and port workers reached a landmark agreement under which port costs will be slashed 25 percent to 30 percent.

Nevertheless asked if Rio could steal a significant portion of the coffee business from Santos over the long term, Mr. Kvassay said, ''I certainly think so.'' He said that, based on their comments to the press, ''Multiportos is to become a very efficient port with very low costs. They are already taking cargo opportunities away from Santos, which has not yet resolved the problem of high costs.'' Mr. Kvassay adds that this will eventually force Santos to lower its port handling costs, and that ''competition will be very healthy for everybody.''