The nuclear plan proposed by Mr. Gorbachev consisted of three broad stages that would culminate in 2000 with a ''universal accord that such weapons should never again come into being.'' It called for the Soviet Union and the United States to start the process this year and for other nuclear powers to join later. Stages and Deadlines

The proposal broadly covered all aspects of disarmament and was based mostly on existing Soviet positions. Diplomats said it differed from previous Soviet calls for total nuclear disarmament largely in fixing stages and deadlines for the process.

In his proposals for the elimination of medium-range missiles in Europe, however, Mr. Gorbachev made what Western experts thought could be a significant departure.

Outlining the first stage of his program, Mr. Gorbachev called for the ''complete elimination of intermediate-range missiles of the U.S.S.R. and the U.S.A. in the European zone, both ballistic and cruise missiles, as a first step toward ridding the European continent of nuclear weapons.'' Moves by Britain and France

At the same time, he said, Britain and France would pledge not to enlarge their nuclear arsenals.

The stance appeared to resemble the offer that President Reagan made, and the Soviet negotiators rejected, at the Geneva talks on medium-range arms, which collapsed in November 1983 when the Russians walked out. Mr. Reagan proposed in 1981 that the United States would abandon plans to deploy new medium-range missiles in Europe if the Russians dismantled their SS-20 medium-range missiles, a proposal that came to be known as the zero option. Moscow, however, insisted that it should maintain enough SS-20's to counter the 162 nuclear missiles in the British and French arsenals. The talks faltered, the Americans began deploying new missiles and the Russians walked out.