VIENNA, Austria (AP) _ Greenpeace environmental activists climbed atop Vienna's landmark Ferris wheel and unfurled an anti-nuclear banner today, the second day of an International Atomic Energy Agency conference.

The 113-member U.N. agency, meeting in a special session prompted by the April 26 Chernobyl nuclear accident in the Soviet Ukraine, was expected to adopt accords on the early notification of nuclear accidents and emergency aid in atomic disasters.

Four Greenpeace members scaled the towering 200-foot-high Ferris wheel and displayed a banner reading: ''Stop nuclear power now - Greenpeace for a nuclear-free future.''

Police tried to get to the protesters by using ladders to climb up the giant wheel, but failed. The attraction in Prater Park in central Vienna was built in 1896-97, and was shown in the movie thriller ''The Third Man.''

Greenpeace officials said the climbers, two Britons and two Austrians, would climb down later in the day.

''We just wanted to make a point, we do not want to cause too much trouble,'' said Elaine Lawerence, a Greenpeace spokeswoman.

Delegates to the IAEA conference, meeting several miles away at the Hofburg Palace, have been discussing two accords aimed at establishing ways for responding to atomic accidents like the one that struck the Soviet nuclear power station at Chernobyl.

The first accord would require countries to inform their neighbors in the event of a nuclear accident that releases radiation across borders.

The second would require nations to provide emergency assistance to any member country that suffered a nuclear accident.

Agency officials have said there is little serious opposition to either accord among any of the organization's member nations.

The U.N. agency's job is to promote the peaceful use of nuclear power and to help stop the proliferation of atomic weapons.

In opening the three-day special session on Wednesday, Direector General Hans Blix said experts have learned important lessons from the Chernobyl accident.

Blix said those lessons could help make the nuclear industry safer.

But the Greenpeace protesters, barred from attending the conference, charged the meeting was an attempt to hide the continuing danger of nuclear power.

The agency was also criticized by U.S. Secretary of Energy John S. Herrington, who said it should be tougher.

Harrington told reporters that the IAEA needed to be more aggressive in monitoring the use of nuclear power worldwide. He also said he was concerned that two Soviet-designed nuclear power plants being built in Cuba may not be safe.

''We would like to know who is regulating the construction in Cuba, who is building them and what features are being used,'' Herrington said Wednesday. He called on the Soviets to share such information with the United States.

An explosion and fire at the Chernobyl nuclear plant 80 miles north of Kiev, the Ukrainian capital, emitted clouds of radioactivity that eventaully spread over the world.

At least 31 people died in the Soviet Union as a result of the accident, and hundreds were injured.