MOSCOW, JAN. 22 -- President Mikhail Gorbachev sought tonight to pin political responsibility for violent actions by Soviet security forces on the secessionist governments of the Baltic republics while reassuring the world that his perestroika reform movement remains intact.

Addressing Soviet and foreign journalists in Moscow, Gorbachev promised a "thorough investigation" into the spilling of blood in Lithuania and Latvia over the past two weeks and condemned any attempts to seize power unconstitutionally from democratically elected parliaments there. He demanded, however, that the republics abrogate legislation that contradicts the Soviet constitution.

At the same time, in a step not seen here since the dictatorship of Joseph Stalin, Gorbachev authorized a confiscatory monetary reform to soak up billions of excess rubles. High-denomination notes of 50 and 100 rubles will cease to be legal tender at midnight and will only be exchanged under extremely restrictive conditions.

Conservatives in the Soviet leadership and official trade unions have long demanded such a step, arguing that it will hamper black marketeers and speculators who deal in high-denomination notes. The move was fiercely resisted by free-market economists who fought a losing battle last year to persuade Gorbachev that the goal of restoring balance in the consumer market could be achieved through the massive sale of state assets.

Gorbachev's former economic adviser Stanislav Shatalin accused the Soviet leader today of doing nothing to avert an approaching "economic catastrophe." In an open letter to the Communist youth newspaper Komsomolskaya Pravda, Shatalin said the abandonment of radical economic reforms would severely undermine the chances of gaining significant assistance from the West.

The principal purpose of tonight's highly unusual appearance by Gorbachev at the Foreign Ministry press center appeared to be to quell speculation around the world that he had taken a decisive turn toward Kremlin hard-liners. To underline that message, Gorbachev was accompanied to the press center by one of the Soviet Union's leading reform advocates, Alexander Yakovlev, who was reported recently to have been quietly dropped from a presidential advisory council.

"Neither domestic nor foreign policy has undergone changes," Gorbachev declared, speaking from a prepared text. He went on to express concern that "incorrect interpretations" in Western countries of recent events in the Soviet Baltic republics could jeopardize the thaw in East-West relations since he came to power in 1985.

Gorbachev refused to answer any oral questions from the journalists, who had been summoned to the press center on two hours' notice. He has so far failed to provide any complete explanation for the actions of security forces under his authority, including an announcement by Soviet army paratroops Jan. 13 that a self-proclaimed "National Salvation Committee" had replaced the legally constituted Lithuanian government.

At least 13 civilians were killed in the Lithuanian capital, Vilnius, early that morning after Soviet paratroops stormed a television station and transmitting tower belonging to the Lithuanian government. At least four people were killed in the Latvian capital, Riga, Sunday night after internal security troops loyal to the Kremlin took over the republic's Interior Ministry.

Gorbachev sought to distance himself tonight from the events in Lithuania and Latvia by saying that "any attempts to appeal to the armed forces are inadmissible in the political struggle." He offered "condolences" to the victims' families, but said the "root cause" of the crisis lay in the "unlawful acts" of the republics' parliaments -- "the trampling of the {Soviet} constitution, crude violation of civil rights, discrimination against people of another nationality," a reference to the Russian-speaking minorities in Latvia and Lithuania.

"This is precisely the source of the tragedy, not some mythical orders from higher authorities," Gorbachev said.

Over the past two weeks, Gorbachev has sought to use protests by Russian-speaking minorities and the intimidating actions of the security forces as a means of pressuring the separatist governments of the Baltic republics to adopt more moderate policies. So far, the tactic has met with limited success. The republics' leaders have expressed willingness to pay greater attention to the minorities but have not abandoned their insistence on independence.

Tonight's presidential decree on monetary reform said the measures were aimed at fighting "speculation, corruption, smuggling, forgery, unearned income and at normalizing the monetary situation and the consumer market." Some economists estimate that there are more than 200 billion rubles of so-called "hot money" in circulation, money that would be instantly spent if anything worth buying appeared in the shops.

In November, Gorbachev acknowledged that the government had lost control of the country's finances by failing to balance the budget and allowing the unrestricted printing of bank notes. The man responsible for this situation, finance minister Valentin Pavlov, was promoted to prime minister this month.

The previous government, led by Nikolai Ryzhkov, had pledged never to introduce monetary reform, saying it would undercut confidence in both the authorities and the ruble. The last such confiscatory measure here was ordered by Stalin in 1947.

In a television interview tonight, Pavlov insisted that workers would not be harmed by the reform, which also includes restrictions on withdrawals from savings deposits. He said, "50- and 100-ruble notes are one of the main elements in the {illegal} shadow economy, accounting for more than one-third of the total money in circulation."