Operating along lines laid down by the Kremlin's top spy, the Soviet KGB last year propositioned an Estonian nationalist with a $500,000 inducement to establish a fraudulent front for enticing anti-Russian Estonians into the human-rights movement -- for exposure and imprisonment.

The entrapment offer to 44-year-old Erlik Udam puts into hard action the chilling anti-dissident harangues of top Soviet officials, including Yuri Andropov, a power in the ruling Soviet Polit-buro and head of the Soviet KGB.

As though making a virtue out of the huge financial offer secretly made to Udam by his agents in Talinn, Estonia, in the spring of 1976, Andropov himself delivered perhaps the harshest attack against the dissident movement early this month. With Andropov speaking in Moscow's Bolshoi Theater, party leader Leonid Brezhnev and other top Soviet officials were listening.

"Dissidence has become a kind of profession," Andropov said, "that is generously paid with foreign currency and other tips, which in essence is little different from the way imperialist services pay their agents."

The speech, marking the 100th anniversary of the birth of Felix Dzerzhinzky, notorious founder of the Soviet secret police, was ominous. It was the Kremlin's clearest warning that the October Belgrade Conference (convening to check compliance with the 1975 Helsinki agreements) will do nothing to halt Moscow's attack on the dissident movement.

The KGB's approach to Udam -- news of which was smuggled out of Estonia -- is a classic attempt to subvert an anti-Soviet nationalist with promised riches. It reads like a spy thriller.

Udam uncovered and removed a hidden bugging device in the electric meter box outside his Talinn apartment in March 1975. He was summoned to KGB headquarters and interrogated about a missing "civil-defense device" -- in fact, the bug.

The investigation, under command of a KGB major, ended with this offer to Udam: Give back the bug in return for immunity in a KGB investigation of the Estonian nationalist movement, of which he was a secret member. Udam accepted that offer, then rejected a KGB bid to become an undercover agent.

That was only the beginning. A year later, buoyed by the Helsinki accords, the dissident movement was gathering steam. The KGB major summoned Udam to three long conversations, on April 4, 11 and 14, each in a different location. His proposition: that Udam become (in Udam's words) "a prominent dissident and organize a dissident group."

He offered me money for organizational expenses," Udam says. "On April 4, the sum he quoted to me was between $200,000 and 500,000 rubles" (around half a million dollars). The Udam dissident group would then offer foreign correspondents "information" -- actually only information supplied by the KGB.

Udam said no such dissident group could possibly work and that he himself would risk quick exposure. Instead, testing KGB reactions, he proposed a Helsinki "monitoring" group. These groups, set up by dissident safter the Helsinki Conference, have become a top KGB target. Many prominent "monitors," such as Moscow's Yuri Orlov, are now in jail.

When Udam proposed a monitoring group "in conjunction with Finland," the KGB said there was "no sense in bringing the Finns into the plan." Instead, Udam "must deal with the Americans. They have the money for dissidents," and it would be Udam's job to talk American backers out of that money. He was offered 50 per cent of anything he got.

In the end, Udam said no. He refused to recommend anyone else for what he called "such gross deception." The KGB has not contacted him since.

Adding to the credibility of this chilling story, London Financial Times reporter David Satter had his briefcase stolen last February while riding the Riga-Talinn train. Taken by the KGB, it is known here, was a notebook containing Udam's name. Udam's own account, smuggled from Estonia, tells of that event and states that the KGB boasted it was their "personal achievement" that Satter never was able to contact Udam in 1976.

Planting agents provocateurs amidst dissidents and Helsinki monitors is nothing new. The outrageous charge of treason against scientist Anatoli Scharansky seems to have resulted from a denuciatory letter in Izvestia by Alexander Lipansky, another "dissident" who may be an undercover KGB man.

Moscow has made minimal internal human-rights improvements to ward off attacks at Belgrade: allowing some emigration of dissidents, giving early jail release to 13 Russian Baptists, permitting sale of 29,000 American paperbacks (in English). But behind these cosmetic improvements, the real work is unimpeded: expose and distroy the civil-rights movement, the dissidents and the brave souls who believe in Helsinki.