Seeds from 15,000 bushes, trees and weeds have sat in storage in Peoria, Ill., for up to 25 years, a curious collection of rare and strange plant germs from around the world. Now, the seeds have sprouted a new purpose.

A small boom in scientific interest in "natural" sources of new medicines prompted Agriculture Department researchers to sift through the seeds one by one, testing chemically for biologically active compounds. The researchers succeeded -- they found compounds in some seeds that are powerful anti-cancer treatments. They have found other compounds that are strong pest-control agents. The chemicals are undergoing tests now.

The seeds were collected beginning in the 1950s with the idea that there might be some interesting plants among the hoard, plants that might become new cash crops for American farmers, said Richard Powell, the Agriculture Department chemist who is heading the program.

Few useful new crops were found, "and we had the seeds, so we thought we would test them out," Powell said. Very few anti-tumor drugs are made from plants, he said, but that may be only because few have tried to find plant chemicals active against tumors. Most of the research of the past 30 years has sought chemical agents among the microbes from which antibiotic drugs were made.

An effort to find medicines from sea creatures, carried out by Kenneth Rinehart at the University of Illinois, not long ago turned up a substance in sea squirts that appears so far to be one of the most general and effective of anti-virus chemicals.

Among the seeds in Illinois, the most powerful agent found so far comes from an evergreen called the plumyew, a native bush of China and Japan. In first-round animal tests against a variety of cancers in mice, the plumyew chemical made colon tumors shrink or disappear altogether, extended the life of leukemic mice by at least 300 percent over the length of time they would live without treatment, and doubled the lifetime of mice with the dark-colored and hard-to-treat tumors called melanomas.

There is no certainty that the animal results will hold up in humans. If they do, the plumyew may be a significant new treatment to be placed alongside anti-tumor compounds already in use, all of which have different side-effects and varying powers against different tumors. Tests are expected to begin soon at the National Cancer Institute.

In the People's Republic of China, where folk medicine is taken quite seriously and drugs are not tested thoroughly before being tried on humans, the plumyew chemical was quickly tested after its discovery in Illinois. The Chinese have tested it on several hundred people and report high "cure" rates for patients with leukemia -- up to 80 percent cure rates in some reports, said Powell. He cautioned that the Chinese way of counting cures involves no more than a few months of follow-up, compared to the standard five years in this country.

Altogether the Agriculture Department team, including Powell, Cecil Smith, and David Weisleder, has tested about 1,200 different seeds and found a dozen that inhibit cancer or may be useful as pest control chemicals.

They have found chemicals that are effective against such pests as the corn borer and beetles that thrive in grain-storage bins. Some of the chemicals kill the bugs outright, and some are distasteful to them and may be used to coat and protect crops from the insects. The chemicals have the advantage that, unlike some man-made ones, they break down gradually into common, harmless substances.

To find the effective chemicals in the heaps of collected seeds, the researchers grind up seeds and put them into a solvent such as alcohol to free them from their husks. The alcohol is then evaporated, leaving an array of substances that can be tested, first on tumor cells growing in dishes, then on mice with tumors.