An international panel of nuclear specialists reported today that the Chernobyl nuclear incident "appears to be stabilizing," with the graphite fire in the core extinguished. Radiation is still leaking into the atmosphere but the levels are falling, it said.

The panel, composed of Hans Blix, director of the United Nations' Vienna-based International Atomic Energy Agency, and two other senior IAEA officials, gave the first independent acknowledgement that the Chernobyl situation is under control in a press conference here at the end of a four-day fact-gathering mission.

Their conclusions were based on information provided by Soviet officials and on their own observations during a helicopter tour of the reactor site.

The graphite fires that engulfed the Chernobyl plant almost two weeks ago "have been extinguished," said IAEA nuclear safety specialist Morris Rosen, an American member of the team.

The damaged reactor is emitting "relatively little radioactive releases now," Rosen added, and "the temperatures are decreasing, with the situation appearing to be stabilizing."

Rosen said he had seen some smoke still rising from the crippled reactor during the helicopter ride, but that the smoke was light gray, indicating that it may have come from the layer of sand and other materials dropped on the fire, rather than from a still burning graphite core, which would have produced much darker smoke. He said the other three reactors on the site are not endangered.

Soviet rescue workers are "entombing" the damaged reactor by pouring cement underneath it in an effort to seal the reactor core indefinitely and allow it to cool, Rosen said.

Rosen said that there had not been an actual meltdown, an assessment that contradicts the view of other American scientists.

American experts said that, while molten fuel may not have gone through the floor of the reactor, it is quite likely that some of the fuel did melt, Washington Post Staff Writer Philip Hilts reported in Washington. Harvard University's Richard Wilson said that what occurred might not be called a "meltdown" in the usual sense because the molten fuel may not have run together. But some of the 1,700 separate fuel elements most likely did melt, he said.

Asked if such a meltdown was still possible, Rosen said it "is not completely excluded and cannot be excluded," although "the chain reaction stopped immediately after the accident and never started again."

The entombment process, he said, "is meant to ensure that there is no more . . . melting."

Blix and the other IAEA experts also indicated that the threat of uncontrolled downward burning of the fuel that could melt through the foundation into the ground, the so-called "China Syndrome," had also receded.

Nevertheless, Blix made clear at the press conference that he disagreed with suggestions in the Soviet media that the West was exaggerating the Chernobyl accident.

"It is clear that the radiation consequences of this accident are far more serious than in any accident so far," he said. "The radioactive releases into the environment are much more serious. It is rightly receiving unique attention."

But Blix also said he was "emphatically" satisfied with the data and information that the Soviets eventually provided.

About 80 miles south, in Kiev, Ukrainian officials ordered early summer holidays for 250,000 schoolchildren. Holidays will begin immediately for all school-aged children who are being evacuated and a quarter million others between ages 6 and 11.

Officials in Kiev told foreign reporters today that constantly monitored radiation levels there pose no health danger.

The reporters, returning to Moscow after a one-day trip sponsored by the Foreign Ministry, said anxiety over the incident, but not panic, was evident.

Moscow has agreed to provide the IAEA with daily reports of the radiation levels and other relevant data from seven sites in the country, including one 38 miles from Chernobyl, Rosen said. The data will be passed on to IAEA member countries.

Soviet officials also agreed to send nuclear specialists to Vienna to discuss the causes of the accident sometime this summer, Blix said.

Reactor "temperatures measured through infrared sensing are below the melting point, and are decreasing," he added. But they are still above the 300 degrees centigrade (572 degrees Fahrenheit) reported by Soviet officials yesterday, he said.

Rosen and Blix told a crowded hall of reporters that inconclusive or incomplete information prevented them from identifying the cause of the disaster or the lingering danger to the population and agriculture in the surrounding regions.

The IAEA officials gleaned a few fresh facts about the accident, however. When it occurred, Rosen said, the reactor was undergoing a planned maintenance shutdown and was operating at 7 percent capacity.

The Soviet Union did not report the incident to the IAEA until two days later, Blix said, after radioactivity had swept across Scandinavia, provoking Swedish inquiries.

Soviet authorities have said that they informed the competent international officials "as soon as" they knew about the problem.

Ukrainian officials told foreign journalists that they first informed Moscow of the incident on the day it occurred, April 26, but alerted officials in the Soviet capital about "the full gravity" of the situation only two days later.

"Moscow was told about this [the full seriousness of the accident] on the 28th," said Ukrainian Prime Minister Alexander Lyashko. "It was an evolving situation."

Blix said today that the Soviet Union had not closed nuclear plants of the Chernobyl type following the incident, except at Chernobyl itself.

"They seem to have found nothing so far in their research to lead them to close the other reactors," Rosen added. "We have been told there are no other cases."

A western diplomat today insisted, however, that at least four other graphite-moderated reactors, in addition to the four at Chernobyl, had been shut down since the accident.

He said there are 15 such reactors in the Soviet Union, out of a total of 41 facilities.

The diplomat said there are questions about whether the other models are operating at full capacity. Last week, there were signs that they too had been throttled back, perhaps for maintenance tests, he said.

The IAEA officials said today that several of the 204 victims of the incident who are hospitalized in Moscow have undergone bone marrow transplants.

In Kiev, officials said that 20,000 people had been tested for radiation, but no cases were found in which radiation had threatened health. Rosen told journalists in Moscow that the water quality in Kiev conformed to health standards throughout the incident.

Blix said discussions his delegation held with Soviet officials were "very frank and very open." But he said that several IAEA member countries had stressed that the radiation levels resulting from the incident should have been released earlier.

After returning to Vienna later today, Rosen told The Associated Press: "One can say certainly the situation is stabilizing, and perhaps one can be optimistic . . . I would use the word perhaps. Certainly the information I have just given you would lead you to certainly feel comfortable."

Blix interjected: "Well, we don't want to go too far."