NEWS ANALYSIS : Gorbachev Pressured by Left, Right to Take Firm, Crisis-Ending Steps : Soviet Union: He will report to the national legislature today on the state of the nation.

In a mounting challenge to his leadership, Soviet President Mikhail S. Gorbachev is coming under intense pressure from both radicals and conservatives to take decisive actions that would pull the country out of its deepening crises.

Across the political spectrum, demands are growing for measures that will reverse the disintegration of the national economy, halt the breakup of the Soviet Union as a federal state and provide the country’s new political institutions with the power they need to deal with such crises.

Gorbachev, who is general secretary of the Soviet Communist Party as well as the country’s president, is expected both to lead and to command, to exercise his political and moral authority and, if necessary, to rule by decree to achieve these goals.

Summoned to report on the state of the nation today by the Supreme Soviet, the country’s legislature, Gorbachev faces what a commentator for the official news agency Tass called “the moment of truth” as deputies demand resolute action to end what it described as “the progressive paralysis of power.”

Boris N. Yeltsin, the populist president of the Russian Federation, is expected to reply to Gorbachev this morning in what could be a showdown--or a dramatic reconciliation--between the country’s two most powerful leaders.

Yeltsin called on Gorbachev to form a “coalition government of national unity” at a five-hour meeting last Sunday and to work out guidelines for the sharing of political power. He claimed that Gorbachev agreed in principle, and the president, while not replying directly, said later they had no serious differences.

Despite the magnitude of the crisis and the growing demands for more forceful measures, Gorbachev’s tactics so far appear to consist of incremental decisions and cautious moves that, while perhaps sound, have failed to give people the sense of a breakthrough and have infuriated both radicals and conservatives.

On the left, a group of 22 radical intellectuals warned the president in an open letter Thursday that “unless decisive, urgent measures are taken, tragedy will be unavoidable.”

They urged him to use his sweeping powers to rule by decree to accelerate the country’s democratization, give farmers their own land to increase food production and reduce the authority of the Communist Party, the military and the security services.

“We appeal to the president . . . either use your powers to take decisive measures or resign,” said the group, which included political scientist Oleg Bogomolov, historian Yuri N. Afanaseyev, economist Pavel Bunich, sociologist Tatyana Zaslavskaya, novelist Ales Adamovich and film-makers Elem Klimov and Tengiz Abuladze.

An opinion poll published with the letter in the avant-garde weekly paper Moscow News showed that 62% of the population feared famine in the months ahead and 33% believed a right-wing coup was possible.

On the right, members of the Russian Communist Party’s Central Committee on Thursday blamed Gorbachev for what speaker after speaker described as a nationwide crisis, with food in such short supply that even rationing, now being introduced in Leningrad and planned for Moscow, may not prevent starvation.

“Mr. Gorbachev should be called to account,” said a party leader from a large factory in the city of Kuibyshev, substituting mister with much emphasis for the normal party title of comrade when he referred to Gorbachev. “Where is Mr. Gorbachev’s leadership taking our Soviet Union?”

Military officers told Gorbachev to his face earlier this week that he was quickly losing their backing by allowing politicians to continue debating reforms long overdue, permitting leftist attacks on the armed forces and failing to preserve the Soviet Union’s integrity as a state.

“Any further delay in addressing these problems will be lethal,” one officer told Gorbachev, borrowing a phrase that V. I. Lenin, the Bolshevik leader, had used on the eve of the Russian Revolution in 1917.

Marshal Sergei F. Akhromeyev, Gorbachev’s own military adviser, accused the leadership of inaction and cowardice in the face of “a superbly coordinated and increasingly brazen onslaught by anti-socialist forces.”

The Supreme Soviet demanded Wednesday that Gorbachev report on what actions he is taking to resolve the country’s multiple crises. Alarmed by the already severe food shortages, the dearth of consumer goods and the ineffectiveness of rationing, deputies want a step-by-step outline of Gorbachev’s plans.

“The president is expected not only to honestly analyze the situation in the country, but also to offer specific proposals to stabilize it,” a Tass commentator wrote Thursday, noting the mounting anger among lawmakers over Gorbachev’s failure to use the power to rule by decree that he had asked for a month ago.

Gorbachev, speaking Thursday with Achille Occhetto, the visiting leader of the Italian Communist Party, acknowledged the “sharpened discussions” but gave no indication that he intended to change his approach.

“The future of our country for many coming decades depends on the decisions currently being worked out,” Gorbachev said, according to a Tass account of his meeting with Occhetto. “The primary task is to consolidate society while avoiding the extremes.”

Gorbachev said his first priority is agreement on a new treaty uniting the country’s constituent republics on a basis that recognized both their sovereignty and their mutual dependence. This would be the foundation for further political and economic reforms, he said.

The next 18 months will be crucial for perestroika, or restructuring, as the reform program is known, Gorbachev told Occhetto. During this time, the country will be trying to switch from a centrally planned system to a market economy; Soviet economists expect widespread unemployment and rising inflation in the transition.

Although he received broad authority when the Soviet constitution was amended in March to create an executive president, Gorbachev asked for additional emergency powers to push through the reforms. He can rule the country by decree, dismiss the government, dissolve Parliament and impose emergency rule.

“As you demanded, you were given special powers,” the intellectuals wrote in their letter to Gorbachev. “You can either use them to build a dictatorship or to deepen democratic perestroika. Dictatorship will lead you and the whole country to destruction.”