Human rights champion Andrei Sakharov warned on his first trip to the West that Soviet leader Mikhail Gorbachev's reforms face a domestic backlash but dismissed the personal risks of continuing his outspokenness.

"If perestroika does not succeed, then the question of my return to (exile in) Gorky is totally insignificant," Sakharov said through a translator Monday. Gorbachev released Sakharov from internal exile nearly two years ago.Perestroika, the restructuring of the Soviet economic and political system, is "at a very critical phase," the 67-year-old Nobel Peace Prize winner told reporters during a two-hour news conference.

He said there are "sharp debates in the press and at all levels" over political and economic issues. "The fate is being decided of which direction our development will go," said Sakharov.

"The West must not fear perestroika. A greater danger to the world as a whole would be the failure of perestroika," he said, warning that failure could strengthen his country's military-industrial complex and result in an expansionist foreign policy.

Sakharov said arms control negotiations between the Soviet Union and the United States are at a critical juncture, with both sides considering 50 percent cuts in their strategic arsenals. "It is an extraordinary opportunity," he said.

Monday was Sakharov's first full day outside the Soviet Union. He arrived Sunday night from Moscow to begin his two-week trip to the West by visiting relatives in the Boston area. His wife, Yelena Bonner, remained in Moscow.

Sakharov was scheduled to undergo a heart examination at Massachusetts General Hospital today or Wednesday, then fly to Washington on Thursday night to take part in a board meeting of the International Foundation for the Survival and Development of Humanity.

Sakharov has accepted an invitation to meet President Reagan at the White House on Nov. 14, presidential spokesman Marlin Fitzwater told reporters aboard Air Force One as Reagan returned to Washington from California on Monday night.

Yevgenii P. Velikhov, foundation chairman and vice president of the Soviet Academy of Sciences, said the organization has begun work on nuclear weapons verification and environmental protection and hopes to sponsor an exchange visit of 2,000 children between the Soviet Union and the United States next year.

Sakharov, a physicist who helped his country develop the hydrogen bomb in the 1950s, won the Nobel Peace Prize in 1975 for his fight for human rights. In January 1980, he was banished to Gorky, an industrial city about 250 miles from Moscow that is closed to foreigners, for opposing the Soviet invasion of Afghanistan. In December 1986, Gorbachev allowed him back to Moscow.

Sakharov declined to comment on Tuesday's U.S. election, but said he respects the United States for its democracy, work ethic, dynamism, self-criticism and generosity.

"The phrase you often hear in the U.S. is, `Can I help you?"' he said. "That is something you hear mainly on the street or in stores, but it also appears (in U.S. behavior) on the international stage."