Abnormal amounts of the radioactive element plutonium were found last year in the bodies of some natives who had returned to Bikini Island after that atoll, once the site of atomic tests, was declared safe by the federal government in 1969.

Tests in 1977 also found for the first time that the Bikinians absorbed significant amounts of radioactive strontium and cesium in their bodies - more than the level considered safe over an extended period by U.S. experts.

Strontium and cesium had been found in the natives' physical systems before, but in much smaller and theoretically safer amounts.

Plutonium, strontium and cesium all accumulated on Bikini in the fallout from atomic tests conducted more than 20 years ago.

They are present in the air, so the Bikinians inhale them. They also are present in the islanders' food; vegetables and fruits from the trees take up the radioactive elements from the soil.

Finding of these three elements last year in the systems of the Bikinians triggered a decision this year to move the natives off Bikini Island and relocate them, perhaps to another South Pacific atoll.

All three elements are recognized as cancer-causing agents. Scientists disagree on what dosage over what period of time can lead to the disease.

According to Interior Department sources, none of the present Bikini residents appears to have become ill from inhabiting the island.

They are now being fed entirely from food and water brought in from the outside monitored by physicians.

In material presented to a House Appropriations subcommittee recently, the Interior Department said the proposed relocation - for which the department wants $15 million - was protected by a decision that Bikini Island "should not be used for agricultural purposes . . ." No mention was made of the radioactive accumulations in the natives' bodies.

In 1968, President Johnson announced that the Bikini people, who had left their home atoll in 1946, could return after the islands had been cleaned up and rehabilitated.

A 1969 survey, conducted by the Atomic Energy Commission, found Bikini Island "with virtually no radiation left," according to an AEC spokesman at that time.

Bikini Island was plowed up, radioactive topsoil removed and 50,000 new coconut trees panted. On the lagoon side of the island, 40 cement homes were constructed.

Although the islands were said to be safe, government scientists knew there were still contaminated areas and thus the possibility that food grown on the island would have higher-than-normal levels of radiation.

The assumption was, however, that these higher levels would still be safe.

To keep track of the natives who had returned, the Atomic Energy Commission, now the Department of Energy, arranged to have periodic medical examinations given at Bikini. One was done in 1974 and did not turn up anything unusual.

About that time, however, the Bikinians hired a lawyer to help them win payments from the U.S. government for damage caused them and their atoll during the nuclear testing.

The lawyer pressed for additional health tests and for an aerial radiological survey of Bikini which, among other things, would locate even small pockets of dust-sized plutonium.

Ground surveys made in Bikini in 1975 pointed out contaminated areas in the interior of the island. They were considered "hot" enough so that government scientists ruled them out as potential silts for additional housing.

Some wells on the island were also found to have water with too much radioactive strontium in them to permit use for drinking.

These surveys, however, did not locate specific plutonium pockets.

In December 1975, the Bikinians presented their case to a federal judge in Hawaii. At that session the federal government agreed to undertake an aerial survey of the atoll. But the survey has not been made.

The Defense Department initially balked at paying the $2 million estimated cost. That was to cover the outfitting of a special ship and the helicopters that would fly from its deck to perform the measurements.

Also involved was the Department of Interior, which adminstraters the Trust Territory in which Bikini is located, and the new Department of Energy and its predecessor agencies. They had supervised the nuclear testing and would provide the equipment and personnel for the survey.

Two years ago, the Office of Management and Budget moved into the fight among these agencies, determining that Interior should seek the funds and reimburse the Navy for use of its ship and helicopters.

Last year, in a supplemental money bill, Congress approved $2.1 million for a radiological survey of Bikini and other Marshall Island atolls that were exposed to radioactive fallout during the 1946-1958 Pacific atmospheric tests.

The only atoll that has been surveyed is Enewetak. That aerial survey was done in 1972, as part of preparations for returning the natives to their homes.

The Enewetak cleanup did not begin until last year and one of the first steps being undertaken is locating and removing plutonium pockets that were disclosed by the aerial survey. In the interim, the few Enewetak people who have returned to the atoll are being kept from the plutonium-contaminated areas.

Although the funds have been approved, the Bikini survey date still has not been set. According to Interior and Energy Department sources, the Navy is now saying that the $2.1 million is not enough to cover costs.

Meanwhile, on Bikini, the natives don't know which areas on the island to avoid so as to miss possible plutonium contamination. Plutonium dust, deposited in the soil, can easily be stirred into the air and then inhaled, according to government scientists.