MURUROA, French Polynesia (AP) _ A Greenpeace ketch dropped anchor 30 miles off France's nuclear test site to await other vessels in the protest flotilla.

The French naval tug Revi circled the Vega less than half a mile away. A French military helicopter carrying reporters flew low over the 40-foot sailboat.

Leading the protest at Mururoa Atoll will be the Greenpeace, a converted ocean-going tug that replaced the Rainbow Warrior, which was the environmentalis t group's flagship until French secret agents sank it July 10 in the Auckland, New Zealand, harbor.

The largest opposition newspaper in Paris, Le Figaro, reported Friday that President Francois Mitterrand knew and approved of plans to sink the Rainbow Warrior, which was preparing to lead the protest.

Mitterand's government acknowledged secret service responsibility for the sinking last month, after weeks of revelations about the affair in the French press. The defense minister and the secret service chief were replaced.

Two French agents are jailed in New Zealand awaiting trial.

Le Figaro said, without citing its sources, said the decision on the attack was made in June in a high-level meeting at the presidential Elysee Palace attended by the defense minister, chief of the secret service and presidential adviser Francois de Grossouvre.

It was ''not believable'' that de Grossouvre failed to inform Mitterrand of the sabotage plans, Le Figaro contended.

Three other protest vessels - the Breeze, Alliance and Varagian - will join the Vega and Greenpeace at Mururoa.

Mitterrand has ordered the navy to prevent interference with nuclear tests at Mururoa ''by force if necessary.''

The Greenpeace is expected to arrive Saturday and the Breeze over the weekend. The Vagarian started late and is weeks away.

Bernard Gerard, France's high commission for French Polynesia, said the navy would intervene if necessary to keep the protesters away from the testing site. Greenpeace spokesmen have said the flotilla will take a position just outside French waters.

The French frigate Balny is shadowing the Greenpeace and four other navy ships also are in the area, including a light transport with a helicopter pad. Two fixed-wing aircraft and five helicopters are in the French force.

''We are not going to make war,'' said Vice Adm. Rene Hugues, commander of armed forces in French Polynesia. ''We are going to carry out an operation of maintaining order.''