Ricardo Alarcon, head of the Cuban legislature, espoused the last argument for reporters Wednesday, one day after lawmakers created a new class of ``counterrevolutionary crimes and stiffened jail terms on common crimes.

He called the Jan. 5 measures -- increasing U.S. aid and contacts with nongovernmental groups in Cuba -- the latest chapter in Washington's ``systematic aggression against Havana. And he said the new law would stop subversion.

``We know of no opposition other than the one fabricated by the United States, Alarcon added, in effect arguing that since all Castro opponents are U.S. puppets, Havana needed a law to treat them all as criminals.

Alarcon seemed to answer one question: Why Cuba had resorted to such a harsh measure when the many foreign friends it gained after Pope John Paul II visited 13 months ago have been calling for a political opening.

But Alarcon's answer did not convince a number of U.S. experts on Cuba who offered myriad explanations and agreed only on this: Havana had enough laws on the books before Tuesday to silence all opponents.

``The government doesn't really need a pretext from the U.S. to crack down on internal dissent. They've been doing that since the day they rode into Havana, said Richard Nuccio, White House point man on Cuba in the mid-1990s.

Street crime increasing

One group of Cuba-watchers argues that the Cuban government was essentially concerned about the rising tide of street crime, and decided to garnish a get-tough-on-crime bill with a gratuitous warning to dissidents.

``Officials cast dissident political behavior as criminal, so from their point of view this is a crackdown on criminality, said Lisandro Perez, head of the Cuban Research Institute at Florida International University.

Nuccio sees it differently. Castro, he argues, may well be trying to spark a crisis in Havana relations with a Clinton administration bent on promoting more U.S. people-to-people contacts with Cuba.

``Cuba prefers a great deal of hostility in its relations with the United States. That's the kind of situation it can manage most easily, by simply tightening controls, he said.

Crises with United States

Proponents of that argument can point to the past. Castro instigated crises in bilateral relations after receiving friendly advances from Presidents Ford in 1976, Carter in 1980 and Clinton in 1994.

None of the above arguments focuses, however, on what it is that Cuba fears.

The dissident movement remains small and deeply fractured, and the so-called independent journalists, targeted by many of the law's provisions, total an estimated 40 people in a nation of 11 million.

``If these people make the government scared, you have to wonder why, said Ruth Montaner, a Miamian who receives U.S. government aid to publish the reports of several dissidents in Cuba.

That is perhaps the hardest question to answer in a country where the Communist Party rules and censors the media. Yet there have been some hints, increasing over the past six months or so, of what Cuba fears:

``There's a sense of erosion, said one U.S. government official in Washington who watches Cuban developments. ``It's a sense of a slow slide, of little movements of the mechanism that are always going backward.