“BUCHANAN, N.Y. – A drop of radioactive water leaks every minute from the pool that stores the spent fuel rods at Indian Point 2 here. The water is captured in a plastic sheet and then channeled into a plastic bottle for disposal. It adds up to a quart or two a day.

Federal officials and the plant’s owners say there is no danger from the leaking water, which contains tritium, a radioactive form of hydrogen. But plant operators have still not pinpointed the source. And because the plant was built when detection systems were not required, the leak went unnoticed until discovered almost by chance when workers excavating around the pool noticed dampness in the surrounding dirt.

The leak, which was found in September, has been the latest worry for local officials and nearby residents concerned about the Indian Point nuclear reactors. It comes on top of repeated failures in tests of the plant’s sirens, which are meant to warn of an emergency. Federal security experts also began a reassessment of the plant’s security in September, which they have declined to discuss.

“It added on to the other issues that we have with Indian Point, like the sirens,” Susan Tolchin, a spokeswoman for Westchester County, said of the leak. She also questioned whether the leak was the only one.

Plant officials have been searching for the source of the leak for the past two months. They have lowered remote-controlled cameras into the 35-foot-deep pool that stores the plant’s spent fuel rods, and they even sent a diver wearing radiation monitors to look at flaws found by the camera for evidence of the leak, with no luck.

While there is no assurance that the leak can be fixed, Don Leach, a project manager at Entergy Nuclear Northeast, which owns the reactor, said, “We are going to do everything we can to get there.” Monitoring wells are also being drilled to detect contamination.

“We’re required to monitor and control our releases, so this is something we have to deal with,” said Don Mayer, a radiological engineer who has been involved in finding the source of the leak. Even so, he said, from the standpoint of the environment, health risks and safety risks, it is almost negligible. “The offsite dose is essentially zero,” he said.

Indian Point’s first plan for stopping the leak was to bring in a diver that Entergy hired, Tim Fisher, 39, of Tucson, who said he has been working as a commercial diver for 17 years. His company, Underwater Construction Corporation of Essex, Conn., has sent him into lakes and rivers and to about 15 nuclear plants to repair parts that must be kept submersed to limit radiation. Mr. Fisher examined three spots in the Indian Point pool, but none of them were the source of the leak.

Mr. Fisher goes into the spent fuel pool with a radiation monitor on each arm, each leg, his back and his head. Readings are instantaneously fed to the surface.

After a series of dives, he recently sat with a colleague, Rene Breault, as they dubbed video images of the pool’s inner liner and of Mr. Fisher’s dive onto compact discs. Stuck to the wall near his workstation with a piece of duct tape, a hand-written note showed how much radiation exposure he could absorb before the end of this year. Under the plant’s rule, he is limited to 1,167 millirem, the amount that the average American absorbs in about three and a half years from natural and man-made sources. He said he was unlikely to get close to that amount on this job; in his last dive, he absorbed about 15 millirem, he said.

He professed little concern about working a few feet from the highly radioactive fuel, which is stored in water that acts as a radiation shield. “Whatever it takes,” he said.

He has explored almost all of the pool area that is accessible to humans. Soon Entergy will begin with a smaller camera that can squeeze into the bottom 15 feet of the pool, the area between the side of the fuel rods and the wall. Finding the source of the leak there would be reassuring, company officials say, because they would know where it is, although it is not clear how they would repair it.

Tritium levels above the drinking water limit have been found at only one monitoring well near the storage pool, and no wells in the area are used for drinking water, company officials say. Tritium is produced as a byproduct in nuclear reactors producing electricity. Small amounts are routinely released as plants like Indian Point continuously filter out radioactive contaminants like strontium and cesium from water from its reactors, and release the water.

To put the leak in perspective, plant officials say the two Indian Point operating reactors already legally discharge into the Hudson every year an amount of tritium 18,000 times greater than what is now leaking.

That has not stopped plant opponents from raising concerns about the leak.

Senator Hillary Rodham Clinton, Democrat of New York, recently met with the chairman of the Nuclear Regulatory Commission and called for a “comprehensive plan” to deal with the leak, as well as swifter notification of local officials whenever there are problems at the plant. Earlier this month the commission promised enhanced oversight, Mrs. Clinton announced.“