A few weeks ago Time magazine ran a cover story on Mikhail Gorbachev's glasnost revolution. The question was: ''Is the Cold War fading?'' In at least one respect the answer is, plainly, no. The Soviet Union has stepped up its jamming of Radio Liberty and Radio Free Europe.

Both are independent agencies, funded by the U.S. government but controlled by a Board for International Broadcasting. They are based in Munich. In any given week, RL is broadcasting 439 hours of news and commentary to the Soviet Union; RFE is broadcasting 630 hours to such Eastern European nations as Czechoslovakia, Bulgaria and Hungary.

These are lifelines of freedom. More than a thousand employees, many of them e'migre's, work at the RL/RFE headquarters. They broadcast in 22 languages, including such obscure tongues as Turkmen, Uzbek and Tadjik. Another 500 Portuguese, Spanish and German employees work at five transmitter relay stations. It is a big operation.

It draws a big audience. During an average week, judging from the agency's surveys among Eastern European travelers, RFE reaches roughly 33 million listeners. An estimated 60 percent of Polish and Romanian adults tune in every week. The audience is much smaller in Bulgaria and Czechoslovakia because Soviet jamming is more effective there. Roughly 20 million persons in the Soviet Union manage to tune in to RL every week.

The masters of the Soviet Union despise the two broadcast services. Gorbachev and his colleagues agreed in May to stop jamming Voice of America broadcasts. That was nice of them. But the jamming transmitters thus released were turned immediately toward the task of jamming RL/RFE broadcasts. The reason, said Soviet spokesman Yuri Gremitskikh, is that Radio Liberty's objective ''is to provide information that undermines internal security and stability of our countries.''

What hokum. The RL/RFE broadcasts have nothing whatever to do with ''internal security.'' If straight factual information tends to undermine ''stability,'' the Soviets are confessing to weaknesses beyond ordinary estimation. True, the RL/RFE programs include more than straight news; they include editorial commentary -- sometimes biting -- that supports a dissident line, but it would take a regime as frightened as Gorbachev's to see in such broadcasts a perilous ''undermining'' of Soviet power.

I asked Malcolm Forbes Jr., chairman of the agencies' board, to give me typical examples of the kind of subversive stuff RL and RFE are transmitting. Among the examples was ''Whirlwind of Change in Soviet Cinema.'' The broadcast exposed efforts of the communist regime to throttle creativity by supporting only those directors who hewed obediently to the Kremlin's line. It cheered efforts of Soviet artistic unions to break away from the cultural ''stagnation'' that had existed under Leonid Brezhnev. It criticized those ''conservative and vapid time-servers'' who toadied to the official line on movie production. At least by Western standards, this was tame stuff. But it is the kind of material that is constantly jammed by the fearful flunkies of Mikhail Gorbachev. Glasnost? Openness? The Soviets cannot stand outside commentary even on their movies.

Another broadcast on RL had to do with the easy availability of computers in the United States. The Russian commentator made a small joke. A friend in the United States had asked him what a typical home computer would cost in Moscow.

''Well, as you know, prices in Moscow are all very stable, and this applies to computers as well. A computer like yours would cost you no less than three and no more than 10 years in jail.''

Funny? Such jokes are unfunny in the Kremlin. The Soviet Union is determined that as few as possible of its captive people will be permitted to hear such broadcasts. Gorbachev's jamming cannot be wholly overcome, but with modernized equipment it can be considerably offset.

The Soviet Union employs 5,000 technicians, 2,000 transmitters and an estimated billion dollars a year to jam Western broadcasts. RL/RFE would be happy to have $125 million a year to keep the channels to freedom flowing.