MOSCOW, FEB. 7 -- The parliament of the giant Russian republic voted today to hold a referendum next month on whether to create a popularly elected Russian presidency, a move that could further undermine the authority of Soviet President Mikhail Gorbachev.

The plebiscite on the Russian presidency is one of several questions that will be added to the ballot when Russian citizens go to the polls on March 17 as part of an unprecedented referendum throughout the Soviet Union on the nation's future. Gorbachev earlier had made clear that he wanted the referendum restricted to the single question of whether to preserve the world's second superpower as a federal state.

Russia's leading presidential candidate in a direct election would almost certainly be Boris Yeltsin, a populist ex-Communist generally regarded as Gorbachev's principal political rival. At present, Yeltsin holds the lesser position of chairman of the republic's parliament, though he is given the courtesy title of Russian president.

If Yeltsin became president of Russia by popular vote, he would have an exceptionally strong political base from which to challenge Gorbachev. Although he was elected Soviet president last March by the Congress of People's Deputies, Gorbachev has never faced voters in a contested election.

With a population of 140 million, Russia is larger than all the other 14 Soviet republics combined and contains three-quarters of the country's natural resources. A directly elected Russian president would be able to claim a popular legitimacy unmatched by any other official.

Public opinion polls suggest that Yeltsin, a former Moscow Communist Party chief who fell out with Gorbachev in November 1987, remains the country's most popular politician. But many analysts believe that his popularity could fall dramatically over the next year unless he finds a way to reverse the precipitous decline in the living standards of Russians.

The official news agency Tass predicted today that the Soviet Union was on the verge of large-scale price increases. It said the new government of Prime Minister Valentin Pavlov had decided to scale back subsidies of consumer goods and food that amount to between 130 and 170 billion rubles a year, one-third of the state budget.

Wednesday, in another attempt to portray himself as the leader of the opposition, Yeltsin announced the appointment of a 23-member think tank known as the Supreme Advisory Council. The body includes many of the Soviet Union's best-known reformist intellectuals, including foreign policy specialist Georgi Arbatov, agriculture expert Vladimir Tikhonov and economists Oleg Bogomolov, Pavel Bunich and Nikolai Shmelyov, all former advisers to Gorbachev.

Today, Russian officials announced that bugging equipment had been discovered in a room immediately above Yeltsin's office in the Russian parliament building. The Russian parliament voted to set up an investigation after the offices were inspected by legislators, a Russian prosecutor and two representatives from the KGB, the Soviet secret police.

In Washington, meanwhile, the Senate-House Helsinki Commission announced that a congressional delegation has received visas to visit the three Baltic states and Moscow next week. The delegation will be led by commission co-chairman Rep. Steny Hoyer (D-Md.).