Mikhail S. Gorbachev called Tuesday for sweeping changes in the Soviet Union, including creation of a legislature with real power and a president with duties akin to those of many Western heads of state.

In outlining his new policies, he also proposed that farmers be made masters of their own land to improve the availability of food.It was not immediately clear what the legislative proposals would mean for the post of Communist Party general secretary, the job that makes Gorbachev the most powerful man in the Soviet Union.

Gorbachev spoke of a president of the Supreme Soviet who would chair the defense council and nominate the premier, or leader of the government.

Addressing his party's first general conference in nearly a half-century, Gorbachev said people should be guaranteed the right to privacy ostensibly granted by the 1977 constitution but served notice the party would not brook organized challenges to its authority.

In a 31/2-hour speech opening the conference, Gorbachev also told the 5,000 delegates that reform of state-set wholesale and retail prices "is absolutely necessary," despite widespread concern that the cost of food and consumer goods will increase drastically.

Stopping short of urging the dismantling of the Soviet Union's system of collective farms, the reform-minded Gorbachev proposed "the extensive, countrywide introduction" of a program to permit families to lease farmland from their collective and state farms and till the soil themselves, rather than as part of salaried farm brigades.

Occasionally interrupted by brief applause, Gorbachev told the delegates in the Kremlin's glass and marble Palace of Congresses that his policy of "glasnost," or greater openness, does not mean he will tolerate formation of new political parties that challenge the rule of the Communist Party.

Nor, he said, should glasnost be abused by those trying to redraw political boundaries, an obvious reference to Soviet Armenia's efforts to annex a region belonging to the republic of Azerbaijan.

Rejecting recent calls for more autonomy from delegates representing the Baltic republics, Gorbachev said, "Any obsession with national isolation can only lead to economic and cultural impoverishment."

Gorbachev called for an overhaul of the nation's legislative system to give the Supreme Soviet and the legislatures of the 15 Soviet republics real power. Now, they generally act as bodies approving decisions of the Communist Party.

The Supreme Soviet, the nominal parliament, would become a full-time standing body with fewer than a third of its present 1,500 deputies, and members would be elected - as early as next spring - by a new Congress of Deputies.

The congress would be a new policy-making body similar to the existing Supreme Soviet but expanded to include representatives of various worker and special-interest groups.

Gorbachev's address, broadcast live by Soviet television and radio, is expected to be the basis for discussion by the party delegates, who will meet behind closed doors to consider various resolutions setting party policy.

Delegates have cautioned against expecting great policy changes or shifts in the top party elite at the conference, the party's first since 1941. But they've said the forum would seek to redefine the role in society of the 20 million-member party.