RIO DE JANEIRO, BRAZIL, OCT. 7 -- American and Soviet nuclear experts joined forces today in a virtually hopeless bid to save a 6-year-old girl who rubbed glowing radioactive powder on her body thinking it was glitter.

The girl, Leide Ferreira, was one of 34 persons hospitalized in Brazil's most serious radiation accident, which occurred when a man broke open a hospital therapy machine containing the radioactive powder.

Doctors said Ferreira and two adults had little hope of survival.

Dr. Robert Ricks, director of the radiation emergency assistance unit at Oak Ridge National Laboratory in Tennessee, arrived today in response to a worldwide appeal by Brazil for specialist help.

The Soviet Union, Argentina and West Germany also sent specialists. Another Oak Ridge specialist in radiation contamination, Clarence Lushbaugh, was to arrive Thursday.

Ricks went straight to the Navy Hospital in Rio where Ferreira and nine other patients lay in lead-shielded beds.

The accident occurred in September in the city of Goiania, 600 miles from Rio. Ferreira's uncle, a scrap-metal dealer, broke open a hospital radiation therapy machine with a sledgehammer and gave curious children and neighbors the attractive, glowing powder he found inside. It was Cesium 137, a radioactive isotope commonly used in cancer treatment, but potentially lethal in large doses.

"Apparently the girl even ate a piece of bread while she had powder all over her hands," said Rex Nazareth, president of Brazil's National Nuclear Energy Commission.

Many days passed before the victims began arriving at local hospitals complaining of vomiting, diarrhea and burning skin. The most seriously affected victims have lost their hair and show growing weakness, with sharply reduced production of red blood cells by their damaged bone marrow, officials said.

Doctors said the girl may have absorbed six times the dose that is normally lethal to humans. At least two other victims may have received the equivalent of 33,000 chest X-rays, officials said.