MOSCOW, JULY 15 -- President Mikhail Gorbachev issued a decree today ending the Communist Party's monopoly of state-run television and radio and giving all political groups access to the air waves.

The decree was announced on the Soviet evening news following an anti-Communist demonstration by an estimated 100,000 people in central Moscow. It comes two days after Gorbachev, in apparent reaction to the defections of several high-profile leaders from the party, pledged to work with non-Communists in governing the Soviet Union.

Gorbachev's order said that growing democratization across the Soviet Union "requires a cardinal change in the country's television and radio broadcasting" and that "this or that party, political current or group" cannot claim sole access to air time. It made clear that the government retains ultimate control over television and radio in all 15 Soviet republics.

The new measure, which is considered a major extension of Gorbachev's policy of glasnost, or openness, appeared to be a response to widespread complaints that television and radio have been used to serve the interests of the Communist Party for too long.

Gorbachev already has pushed through measures ending the party's monopoly on power, and in June the legislature passed a press law ending censorship by the party and specifying rights of journalists.

In a country where state officials exercise tight control over what is broadcast on radio and television, the law seemed likely to make a dramatic difference. Ever since television was first offered to Soviet viewers in the 1950s, it has been used to promote the policies and decisions of the party.

Even after Gorbachev came to office five years ago, championing glasnost and a policy of economic and political restructuring, radio or television programs that deviated from traditional party policy almost always were canceled.

More recently, incisive shows spotlighting issues of public concern have been introduced by local television in Moscow and Leningrad. Moscow's "Glimpse" and Leningrad's "200 Seconds" both feature Western-style exposes and investigative broadcasts. But these programs are not shown in provincial areas, where the party has sought to keep a tighter control over the news flow.

Glasnost has encouraged more liberal expression, but so far it has influenced Soviet newspapers and magazines more than the broadcast media. With the impact of television increasing, officials have taken care to control the images projected. So far, those of farm and industrial production and of other party-backed propaganda have predominated.

State committees have set guidelines for television and radio and only groups approved by those committees could have access to air time. As a result, party-sponsored shows dominate the programming.

The new decree gives any party or public organization or local government the right to open a television or radio station as long as it has the funds. It also says that broadcasts on state television should cover the gamut of changes taking place in the Soviet Union.

The new order further states that the Soviet government is the final authority over television and radio in all Soviet republics. "Any acts taken by republican, territorial or regional bodies without coordination with the U.S.S.R. Council of Ministers and aimed at changing legal status" will be considered invalid, it said.

That stipulation clearly was aimed at separatist groups in the Baltic republics and other areas that have claimed Soviet television and radio stations as their own property.

Today's demonstration, estimated at about 100,000-strong, was one of the largest unofficial rallies ever held in Moscow. It was organized to protest the hegemony of the party. Speakers did not mention control of television and radio specifically, but complained about the commanding position of the party.

Coming two days after the closing of the party's 28th congress, the protesters reflected its failure to adopt radical changes, demonstrators said.

The protest was organized by the Moscow Popular Front, the Democratic Russia Bloc, the Moscow Association of Electors, the Democratic Platform and other groups that are challenging the Communist Party's monopoly of power. Protesters met near Gorki Park, in Moscow's center, and paraded to the central square next to the Kremlin.

Banners carried by demonstrators called for the party to disband and turn over its property to the people. Others demanded a depoliticized army and KGB secret police.

Among speakers were theater director Yuri Lyubimov and Oleg Kalugin, a former major general in the KGB who was stripped of his rank and medals June 30 after publicly criticizing the organization. Kalugin, recently embraced as a hero among Moscow radicals, said he had decided to leave the Communist Party.