The Reagan administration wants to pay $100 million to the fledgling Marshall Islands government to settle all claims against the United States by Marshallese whose health and property were affected by nuclear weapons tests in the Pacific between 1946 and 1963.

To get all the allocated money, however, the three-year-old Micronesian government will have to certify to Washington that all claims have been duly considered and that no additional suits will be filed against the United States or its citizens arising out of past nuclear testing activities.

Lawsuits seeking more than $4 billion have been filed on behalf of Marshallese with the U.S. Court of Claims, and others are being prepared. The Bikinians, for example, whose largest island remains radioactive almost 20 years after the last test, are seeking $450 million.

Most of the remaining suits have been filed by a group of California lawyers who went out to the islands and signed up thousands of Marshallese willing to sue the U.S. government for personal injuries allegedly caused by American nuclear tests.

The radiation payments proposal, negotiated with officials of the Marshallese government late last month, is the most controversial section of a pact that will change the status of the Pacific atolls from a trusteeship to free association with the United States. The islanders will vote on the pact Aug. 17. If approved, it must then pass Congress and finally the United Nations before it takes effect.

The agreement appears likely to be approved by the Marshallese, but it faces some problems in Congress, where members with a long-standing interest in the area are concerned about how the radiation payments are to be made.

Just over 200 Marshallese from the atolls of Rongelap and Utirik were exposed to radioactive fallout in 1954 from the test of a 15-megaton bomb more than 100 miles away. In the intervening years, more than 100 of them have developed harmful health effects, including cancer and thyroid abnormalities.

In addition, the island properties of thousands of others--particularly on Bikini and Enewetak, the sites of the nuclear explosions--were either obliterated or heavily contaminated with radiation.

"The United States is trying to buy its way out of its responsibilities," said a Washington lawyer who has represented some of the islanders over the past few years. He was particularly critical of the role given Marshall Islands President Amata Kabua, both in the negotiation of the radiation agreement and in the ultimate distribution of the funds.

Kabua is the son of the iroj or traditional king of some of the atolls involved in the testing. In the mid-'60s, his father took a share of $10,000 that Congress voted each of the Rongelap radiation victims. Kabua himself got other recipients to invest in a business he controlled. The business eventually went bankrupt.

"Kabua has changed," according to a federal official who helped negotiate the agreement. "He was elected by the people and has been doing a good job of operating the government."

In an arrangement worked out by Kabua, the bulk of the $100 million has already been divided up, allotting Bikini $25 million, Enewetak $16 million, Rongelap $15 million, and Utirik $10 million.

The remaining $34 million is to go to individual victims under a system that Kabua and his colleagues will design. Whatever money is left will go to Kabua's government.

A problem with this approach is the nature of diseases that may be caused by radiation. In the case of the Rongelap victims, almost 10 years passed before the first thyroid problem was discovered. Since then, almost all the islanders who were under the age of 10 at the time of the fallout have developed a thyroid abnormality.

Only time will tell whether radiation from 20 years ago will cause health problems in the next generation. Thus it is difficult to say whether or not there will be more claims five or 10 years from now.

In another part of the radiation settlement, the Kabua government will take over operation of special medical programs for exposed islanders and their children, funded by a one-time $30.2 million payment from Washington. Since 1955, when the Rongelap and Utirik islanders were still showing immediate health effects from fallout, these regular medical examinations have been performed by American doctors with federal money.

Regarding land, the largest island in Bikini atoll, the island of Bikini, has been found uninhabitable because of radioactive material in the ground. American experts have estimated it will take another 20 years for the levels of radiation to go down enough to let people live and grow crops on the island again. But such estimates have proved optimistic in the past.

The U.S. government spent almost $110 million to clean up several of the Enewetak islands so they could be resettled. As part of that project, however, one island in the atoll, Runit, was made the dumping groung for large amounts of plutonium and other nuclear debris. Runit was sealed and put off limits for 20,000 years. There is still a question of who would be liable if radiation leaks pose a potential danger to the atoll's lagoon and the fish in it.

Another portion of the agreement that has created problems for some Marshallese concerns rental of Kwajalein atoll for another 50 years. Kwajalein is a key factor in strategic missile testing. Missiles launched from Vandenberg Air Force Base in California travel 4,200 miles to drop their warheads in Kwajalein's lagoon. Monitoring equipment on the atoll keeps track of how the missiles and warheads perform, and also provide data on how an anti-ballistic missile system would work against them.

The Marshallese who own the Kwajalein islands on which the American testing equipment stands are not satisfied with the roughly $9 million per year they are being offered as part of the agreement.

American negotiators had expected the Kwajalein unhappiness, but are quick to point out how fast the funds paid for use of the atoll have increased.

In 1964, Kabua signed a 99-year lease for Kwajalein that called for payment of $200,000 a year. In 1977, the payment was upped to $740,000 a year and remained at that level until 1980, when negotiations on the new agreement began under the Carter administration.

According to one source in the negotiations, the Marshallese expected the price to go up to $1 million and were amazed when the figure offered was $9 million. Now they are saying even that amount is not enough.