WASHINGTON (AP) _ A coalition of citizens' groups sought a court order Wednesday to delay the scheduled Oct. 12 launch of a nuclear-powered probe from the space shuttle.

The danger of plutonium contamination from a shuttle disaster is far greater than the government has admitted, the Florida Coalition for Peace and Justice and two other organizations said in U.S. District Court.

The groups, which filed suit Sept. 28, made formal requests for a temporary restraining order and a preliminary injunction to stop the launch of the Shuttle Atlantis which is to carry the Galileo probe into space.

In a 37-page court brief, the groups said a number of scientists are counseling against making the launch.

Richard Cuddihy, a leading expert on radiation poisoning, wrote the White House last month, saying the launch puts large numbers of people at risk, the court papers said.

Cuddihy also is a member of the Interagency Nuclear Safety Review Panel which is composed of representatives of NASA, the Department of Energy and the Defense Department.

Cuddihy estimated the cost in human lives and cleanup of a Galileo explosion would be many times higher than that admitted by the National Aeronautics and Space Administration.

He recommended that these types of missions be launched on unmanned rockets from remote locations.

The court filing also said that:

- Robert Weatherwax, a leading authority on the dangers of the space shuttle, has called the Galileo launch irresponsible. He estimates the possibilities of an accident and a deadly plutonium release from Galileo are 1-in-350.

NASA says the highest probability of launch area release of plutonium due to a shuttle accident is less than 1-in-2,500.

- Horst Poehler, a longtime consultant for NASA contractors, has challenged the risk assessments of NASA. Poehler said NASA has not made public for comment the assumptions and details of the agency's calculations for nuclear release or individual per person doses of radiation for various types of accidents.

Once in orbit, Galileo is to rocket itself on a round-about voyage to Jupiter. Powering the craft are two radioisotope thermoelectric generators. Each of the RTGs are energized by 24.7 pounds of plutonium-238.

The suit said the Galileo project will condemn thousands of eastern Florida residents ''to a wholly unnecessary and virtual certainty of contracting cancer'' if a shuttle launch accident, similar to the one that destroyed Challenger in 1986, caused the plutonium to be vaporized and spread over the area.

Joining the filing of the suit were the Foundation on Economic Trends and the Christic Institute.