U.S. aid poured into the Dominican Republic today as the official death toll from Hurricane David passed 900.

Civil defense officials said they feared the toll would go much higher when relief workers reached remote parts of the interior that suffered heavy damage.

A giant C5A military cargo plane brought four helicopters for search and rescue missions, a water purification unit from Fort Campbell, Ky. and jeeps, trucks and other equipment. C130 military cargo planes shuttled to and from Puerto Rico, bringing rice, milk, flour, blankets, tents, medicine, electric generators, communications equipment, and rescue personnel.

"The situation is catastrophic," said Civil Defense Director Pedro Justiniano Polanco. "Hunger is starting to be felt by the thousands of country people isolated by blocked roads."

To recovery effort was hampered somewhat by still another storm, Frederic. Though downgraded yesterday from a hurricane to a tropical storm, Frederic nonetheless threatened the Caribbean islands with more high winds, heavy rain and continued flooding.

Meanwhile, agricultural damage already was running into the billions of dollars as the storm hit in full harvest season.

President Antonio Guzman took a helicopter tour of the badly battered southwestern and western parts of the country, where an estimated 60,000 were homeless.

The greatest death toll occurred in the small village of Ocoa where 400 died when raging floodwaters from the Yaque River swept through the church and school where they had taken refuge.

David struck Santo Domingo and the southeast coast of the island of Hispaniola late Friday with winds of 150 miles an hour after destroying the homes of 60,000 people on the Lesser Antilles island of Dominica and killing 22 persons there and 16 on Puerto Rico. The United States began airlifts to Dominica Saturday, and the U.S. Agency for International Development said it was sending enough emergency rations to feed all the homeless for a week

In Santo Domingo, rooftops torn from houses poked out of the flooded Ozama River. Rocks, trees, utility poles and broken glass littered the streets. An estimated 90,000 persons lost their homes.

Government workers and private citizens were trying to clean up the debris and bring a semblance of order to the city of 500,000. Armed soldiers patrolled the streets to prevent looting.

Cars, buses and taxies dodged chunks of torn-up cement and other obstacles in the roads. Lines formed at the few gasoline stations open. A large tank at the capital's oil refinery was destroyed and production was not expected to resume for several days.

The big hotels and restuarants along George Washington Avenue fronting the sea were heavily damaged.

Officials estimated 90 percent of the nation's crops were destroyed by David's howling winds and furious rains. They said damage to buildings and agriculture ranged between $600 million and $1 billion and appealed for international assistance to rebuild the economy.