Panamanians worry Panama Canal is becoming a white elephant

The naysayers said it wouldn't work, and they forecast all sorts of trouble for joint Panamanian-United States operation of the venerable Panama Canal. But 2 1/2 years after the joint arrangement got under way, the 70-year-old waterway is working quite well - and there has even been a slight improvement in the amount of time it takes the average ship to transit the canal.

There is, however, a cloud on the horizon: the number of canal transits is falling and Panamanians are beginning to worry that the canal's best days could be over.

There is a certain irony in this since Panama, which for so long sought sovereignty over the US-built canal, now is assured full control by the end of the century - but by then, the canal may be a white elephant.

The decline in transits began last year and is largely due to the loss of the Alaskan crude oil trade. This oil is now being pumped through the new pipeline that parallels the waterway.

To cope with the resulting drop-off in canal revenue, the canal's board of directors increased tolls by 9.8 percent within the past fortnight. Additional toll increases are possible, canal economists say, as they brace for what could be ''the most severe decline in traffic and toll revenues since 1932.''

For Panamanians, including those who have become members of the board of directors as a result of the new treaties between Panama and the US that govern canal operations, such a decline in canal transits is ominous.

Some observers openly predict that the canal will continue to decline in importance during the rest of the century as additional oil and gas pipelines are built and as rail traffic across North America increases.

If that scenario is played out, it could spell disaster for Panama since it relies heavily on the canal for its economic livelihood. Without substitute revenue, Panama could be hurting seriously by the time it takes over full control of the canal at high noon, Dec. 31, 1999.

This problem, however, has nothing to do with the current Panamanian role in running the canal - and would have occurred if the US has managed to retain full control.

If anything, the waterway is working even better today than ever before. Despite the fact that the canal's locks and channels are 70 years old, they operate virtually as smoothly as they did when installed soon after the start of the 20th century.

Yet the canal's channels are simply too shallow and the locks too narrow to accommodate many of the supertankers and bulk-cargo carriers that now ply the world's oceans. Many shippers find the canal's usefulness increasingly limited.

Although the joint operation of the waterway has proven smooth, the Panamanian members of the board are increasingly devoting their attention more to the future prospects of the canal than to its present operation. This is clear from a reading of their recent speeches to Panamanian audiences.

''Occasionally we disagree on some expenditure,'' Panamanian Vice-President Jorge Illueca said recently, ''but these are small points. What concerns us most are issues relating to the canal's future and of course this worries us more than the North Americans since we get full control of the canal just 17 years from now.''