A Cuban government crackdown on dissent has grown so harsh -- including brief kidnappings, secret jails and a threatened clandestine execution -- that human rights activists are calling it the worst in a decade.

Police briefly detained 304 dissidents, restricted the movements of another 201 and have been holding 22 more for possible trials since early November, Cuba's foremost human rights monitor, Elizardo Sanchez, said Wednesday.

Prosecutors are seeking a 10-year prison term for the government's most prominent critic, Oscar Elias Biscet, and recently won a six-month term for Victor Arroyo, a dissident accused of giving children toys sent by exiles.

The crackdown comes at a time when President Fidel Castro appears increasingly worried about the level of discontent on the island and the recognition that dissidents have been winning in Cuba and abroad.

Police patrols in Havana, which rose dramatically in January 1999 amid government complaints of a growing crime wave, have intensified further since late November, said several residents of the Cuban capital.

``Where two policemen used to stand in a corner, you now have four,'' Sanchez said.

Eight foreign heads of government and foreign ministers made a point of meeting with Sanchez and other dissidents during a summit meeting Nov. 15-16 of Latin American, Spanish and Portuguese leaders in Havana.

Cuban officials deny any crackdown.

``This is an invention, said Luis Fernandez, spokesman for the Cuban diplomatic mission in Washington. ``I know nothing about any such numbers, but my country would never permit the existence of any counterrevolutionary group that could threaten our national security.

Sanchez, a former professor of Marxism considered the most moderate and accurate of Cuba's human rights activists, said his numbers are clear -- 121 brief detentions in November, 141 in December and 42 in January. The numbers for February are running about the same as January, he said.

`WORST IN 10 YEARS'

``Our data makes this the worst wave of repression in 10 years, he told The Herald in a telephone interview from Havana. Sanchez's report is expected to bolster an attempt to condemn Cuba at the annual U.N. Human Rights Commission meeting next month in Geneva.

Sanchez said he was particularly concerned by some of the new and allegedly unlawful methods that Cuba's secret state security police have been using to harass and intimidate dissidents.

Many of those detained for brief periods were not taken to official police stations or jails but to secret ``security houses around Havana in what Sanchez called ``caricatures of kidnappings.'

Police who ordered the 201 dissidents to stay at home or away from Havana during some scheduled meetings of dissidents showed no orders from any judges or prosecutors, he added.

PERMISSION TO LEAVE

In another effort to silence critics on the island, an unusually large number of dissidents have been receiving long-denied government permission to leave Cuba, said Ruth Montaner, a Miami exile active in supporting dissident groups in Cuba.

Cuba -- which has long boasted that dissidents are never tortured, disappeared or murdered, unlike practices in other parts of Latin America -- has also seen a small number of incidents involving violence or death threats.

Brothers Guido and Ariel Sigler suffered broken ribs after a pro-government mob attacked them after a December meeting of their Alternative Option Movement in the north-central town of Pedro Betancourt, Montaner said.

Sanchez said he received a signed complaint from Nestor Rodriguez, head of Youths for Democracy, accusing police of a threatened execution.

THREATENED MURDER

After detaining Rodriguez on Dec. 27 in the eastern city of Santiago, police drove him in the dead of night to an isolated field about 15 miles outside the city while showing him their pistols and saying they were going to kill him, Rodriguez charged. They abandoned him in the field.

Sanchez and several other leading dissidents signed a letter to the government last week demanding proper medical treatment for Marta Beatriz Roque, a jailed opposition leader suffering from a serious ailment.

Roque, Vladimiro Roca, Felix Bonne and Rene Gomez Manzano are serving jail terms ranging from 3 1/2 to 5 years on charges of sedition -- issuing a declaration attacking the Cuban Communist Party's monopoly on power.

``It is a return to the bad old days, where even medical treatment is used as part of the government's psychological war against dissidents, said Montaner, who has kept close tabs on Roque's health problems.

IN ELIAN'S SHADOW

Many of the dissidents complain that the crackdown has been overshadowed by the media coverage of Elian Gonzalez, the 6-year-old shipwreck survivor at the heart of a custody battle between his father in Cuba and relatives in Miami.

``I have never seen a wave of repression so long and harsh that has drawn so little attention from the international media, said Hector Palacios of the Democratic Solidarity Party in Havana. ``We have been forsaken.

But just why the Cuban government launched the crackdown on dissent remains unclear.

Palacios said it may have been triggered by all of the attention the foreign leaders and journalists gave to government critics during the IberoAmerican summit, sometimes jokingly called ``the dissidents' summit.

Others speculate that the trigger was the recent growth in the number and organization of dissidents -- from about 10 dissidents in 1987 to about 1,000 today, aligned with 60 to 80 groups.