With more than 70,000 pounds of raw opium squirreled away in vaults on military bases across the country, Uncle Sam has emerged as the big daddy of drug hoarders.

The opium is deemed essential for national defense, and the supply may soon be explained if a little known federal agency gets its way.

Using authority granted by Congress in 1939, government managers of the national defense stockpile have designated 93 materials -- from chromium to goose feathers to castor oil -- for purchase and storage in amounts considered necessary to meet a gap between normal supplies and assumed national requirements during a three-year conventional war. The only material stocked specifically for a nuclear war is opium, the source of morphine and other pain-relieving drugs.

"We would be up the creek without opium," says Richard E. Corder, director of the national defense stockpile. "There's substantial pain from radiation burns."

According to the Federal Emergency Management Agency, which develops policy for stockpiling strategic materials, the nation wouldn't have enough opium to go around in the event of nuclear war. The agency has set a goal of expanding the government's board of opium to 130,000 pounds.

The value of the opium now in stock -- which was bought 20 years ago largely from India, Turkey and Yugoslavia -- has soared from $5 million in 1960 to $28.6 million as of March 1978.

The emergency agency says its decision to set higher goals for stockpiles of strategic materials was based on "guidance" from the White House National Security Council.

"The new stockpiling goal is only a target," Corder says, "Any new purchases will require specific authorization from Congress."

The Carter administration has ear-marked $170 million in its budget for fiscal 1981, which begins Oct 1, to purchase additional materials for the stragetic stockpile.

Officials say new, higher stockpile goals have been set for the following materials deemed essential to the nation's defense:

Castor oil. The government's new target is 22 million pounds of this viscous, foul-smelling oil for eventual use in making paints and varnishes, synthetic resins and film for shatterproof windows. The castor beans from which the oil is obtained are imported mainly from Brazil.

Goose feathers. About 1.5 million pounds of duck and goose feathers are needed as filling for sleeping bags, boots and other equipment for use in the Arctic. China is the world's principal supplier.

Cordage fibers. Major military uses for hemp imported from the Phillippines and Ecuador include guy ropes, marine cordage and other construction purposes.

Diamonds. Normally used as industrial cutting materials. The government plans to increase its stockpile to 29.7 million carats from 20 million carats.

A strategic stockpile represents a paticular sort of insurance premium -- one whose value alters over time. The United States has made a large paper profit recently on its total stockpile of 93 materials. Its stockpile value rose from $9.5 billion in September 1978 to $13.7 billion this past March, with very little buying or selling.