Scientists attempting to catalog all life in the ocean have counted 15,300 species of saltwater fish, and they said yesterday they expect to find up to 3,000 more by time the project ends in 2010.

As much as the scientists expect to learn, their $1 billion Census of Marine Life, a 10-year effort that started in 2000 and involves several hundred scientists around the globe, will still be dwarfed by the "scarcely imaginable" range of sea life, according to the report, titled "The Unknown Ocean."

Nevertheless, the scientists expect to produce an oceanic Who's Who that is unprecedented in its scope and detail, they said in an announcement at the Smithsonian Institute in Washington D.C.

"We think by 2010, for the first time we really can have a picture of life in the oceans from top to bottom," said J. Frederick Grassle, director of Rutgers University's Institute of Marine & Coastal Sciences and one of the leaders of the census. "We think it's worth doing, it really can be done and the results are really encouraging."

The census is funded by the Alfred P. Sloan Foundation, and various government agencies, universities and other organizations around the world.

In their first report, the scientists attempted to sketch out what humans know about sea life, what they can figure out and what is unknowable. All three categories were described in dizzying terms, but the last was the largest.

For example, the scientists found that in 3 cubic meters of a coral reef in the South Pacific, there were 130,000 mollusks -- a phylum of invertebrates that includes shellfish -- belonging to 3,000 species. If all the mollusk experts in the world worked on describing just that sample, they would all be retired long before they were finished, the report said. That one reef is hundreds of kilometers long, and it contains much more than just mollusks.

The range of sizes confronting the census tortures the imagination. The blue whale weighs 100 million times more than the shrimp-like krill they eat, and the krill weigh about 50 trillion times as much as the bacteria they eat, the scientists reported.

Fish are still being discovered as fast as they were a century ago, the scientists found. Since 2000, some 600 previously unknown species have been discovered, according to the report. There are about 20,000 knowable species out there, they said.

Other animals and sea plants are being cataloged at a rate of 1,700 a year. The scientists could only estimate the number known so far, and placed it at about 210,000. The total number in existence could be 10 times that, they found.

The scientists are not just combing the world's water-related paperwork. They are getting wet -- diving deep into the ocean in the latest submersible craft, tagging fish, sharks, turtles and seals and tracking them with satellites, and exploiting the techniques and knowledge of the fishing and oil industries to map unknown oceanic expanses.

"We have tremendous technologies and many people who are working globally with us to put this together," said Ronald O'Dor, a squid expert from Nova Scotia and the chief scientist of the census.

Frequently, they are confronted with an inhospitable workplace. The dark zone of the ocean, below 200 meters, routinely outstrips the limits of science with its crushing pressure. One tiny, unrecognized creature a census-taking scientist saw and retrieved deep on the Midatlantic Ridge disintegrated completely by the time it reached the surface.

Nevertheless, the scientists have produced important successes in their first three years, they said.

Off California, they have launched an underwater observation system to tag and track salmon, which should provide new insights into migration. Off the Florida Keys, they discovered a bright red species of sponge they nicknamed the "rasta sponge." Chemicals found in it may be used to treat tumors, the report said.

The scientists hope their work will identify the best breeding spots, help governments regulate fishing and determine how damaging pollution and global warming are to the seas.

The project leaders divided the ocean into six realms. They dubbed the near shore the Human Edges -- it's the zone science already understands best, but that nonetheless contains more than 6,000 unclassified species.

The sides and bottom of the vast bathtub that is the ocean were dubbed the Hidden Boundaries. The edges contain speeding currents and trenches that plunge down several kilometers; the center plains are desert-like expanses blanketed by living and dead particles that float to the bottom in something resembling a never-ending snowfall.

The Central Waters fills the bathtub and teems with meadows of plankton and millions of swimmers of all sorts, in the sparkling water near the surface and pitch-black depths.

The Active Geology category includes volcanoes and deep-sea vents that spew gases from the liquid magma at the planet's core. The vents are crawling with microbes that have evolved to survive the high temperatures.

The Ice Oceans -- the Arctic and Antarctic -- were their own category.

The last was the Microscopic realm, the sea's smallest creatures. Their cumulative weight makes up 90 percent of the weight of all the ocean's living things, the scientists found. A goal of the project is to determine if overfishing and pollution has tipped the scales even more toward the tiny creatures.

"We will know better whether the size spectrum of animals in the ocean is changing," said Jesse Ausubel, program director of the census. "Are small animals replacing the large?"