President Reagan announced yesterday that the United States will resume participating in negotiations for a law of the sea treaty, but that major elements of the draft treaty concerning mining the vast mineral wealth of the ocean floor are unacceptable.

Reagan, who abruptly pulled out of the 8-year-old negotiations last March, said that the United States wants a greater role in decision-making on deep seabed mining and stronger protection for American mining interests.

The U.S. withdrawal last year shocked the other 157 nations that were assembling in New York for what was expected to be the final session of the long and complicated negotiations.

Now, Assistant Secretary of State James Malone, the chief U.S. negotiator at the next session, which opens March 8 in New York, said the United States is seeking influence "commensurate with our interests and concerns."

He said that did not mean a U.S. veto over plans for harvesting the estimated 1.5 trillion tons of nodules rich in copper, nickel, manganese and cobalt that rest on the seabed.

"I mean the United States has influence and impact in this area that it must have in view of its interests, not only in this kind of international organization but indeed in the development of the deep seabed," Malone said.

The United States is concerned that the proposed international authority that would be established under the draft treaty would make policy on a one-nation, one-vote basis and that the executive council that would make day-to-day decisions affecting access of U.S. miners to the seabed would not have a guaranteed permanent U.S. representative.

Singapore's ambassador to the United Nations, T. B. Koh, the president of the Law of the Sea Conference, has said that a demand for major changes in the draft "would be impossible to accommodate."

Malone told reporters at the State Department that "I think we have a realistic chance" of winning approval of the changes Reagan wants at the bargaining table.

The United States is determined that a treaty should have a "pro-development thrust" and should not have the previously agreed-upon limits on production, Malone said. These limits were insisted upon by metal-producing nations, led by Canada, which want to protect their domestic mining industries.

At the core of the complex arguments over drafting a treaty have been two issues: seabed mining and navigation rights.

The draft that was on the verge of being completed last March represented a trade-off for the United States. In exchange for guaranteed rights of navigation and overflight on the high seas and through straits that the Pentagon is eager to have, the treaty gives developing nations a share of the wealth of the seabed.

Malone made clear that the United States thinks that share is too large, but he also cited the importance of navigation rights as the reason the administration has decided to return to the negotiations.

"The treaty as it currently stands would not be ratified by the Senate," Malone said.

Reagan said that in order for a treaty to be acceptable to the Senate it should not contain provisions for the mandatory transfer of privately developed technology to Third World nations nor should it provide for participation by, and funding for, national liberation movements.

Malone said that the other industrialized nations are sympathetic with Reagan's new position.

Malone was asked whether he foresees a problem for development of the seabed if the negotiations break down and there is no treaty. Without a treaty, mining consortia would have no clear title to ocean mines and banks would be unlikely to lend them the huge amounts of money necessary to set up a mine. Malone said he was aware of possible difficulties in obtaining financing in the absence of a treaty.