PAPEETE, Tahiti (AP) _ France detained two young Greenpeace activists who paddled into the waters around one of its South Pacific nuclear testing sites, the environmental organization said.

New Zealanders Daniel Godoy, 22, and Daniel Salmon, 25, were being questioned Thursday at Mururoa Atoll, one of two French test sites 750 miles southeast of Tahiti, Greenpeace said.

Also Thursday, France released two other Greenpeace activists arrested two days earlier at the other test site, Fangataufa Atoll.

The activists, New Zealander Rachel Sanson and Belgian Roger Gregoor, said they observed preparations for a nuclear test as they cruised around a lagoon at the atoll on an inflatable speedboat.

Sanson said they got as far as a drilling rig in the lagoon, which apparently had been used to sink a shaft for the nuclear test.

``It was eerie, there was almost nobody there, until they finally arrested us,'' she said. ``We were afraid the second test might go off underneath us.

The two were flown by helicopter to Mururoa, where they said they were interrogated for 17 hours.

Greenpeace spokeswoman Audrey Cardwell, aboard the schooner Manutea off Mururoa Atoll, said the activists expect France to detonate a 150-kiloton underground nuclear blast at Fangataufa Atoll.

France resumed what it said would be an eight-blast series of nuclear tests Sept. 5 with a test at Mururoa.

The testing has sparked protests from many countries. The Maritime Workers' Union of Australia said today it would ``frustrate and delay'' shipments of uranium from Australia as long as France continues the tests.

Paris warned Australia such action would cause it to cancel contracts to buy Australian uranium worth $54 million, the Sydney Morning Herald reported today.

Australia reportedly told the French ambassador that economic retaliation had no place in the dispute.