BY NANCY SAN MARTIN

  Cuba's communist-run government announced Tuesday night it had rounded up several dozen opponents and slapped new restrictions on the movements of American diplomats here as already bad relations between the two countries further deteriorated.

  An official statement read on state television's evening news program said that Cuba's actions were the result of "the shameful and repeated attitude by the chief of
  Washington's diplomatic mission in Havana, James Cason, to foment the internal counterrevolution.''

  Veteran human rights activist Elizardo Sanchez said by telephone late Tuesday he had confirmed the detentions of at least 10 dissidents and was working to confirm
  reports of another 20 or so picked up by state security agents.

  The announcement of restrictions on American diplomats here was the Cuban government's first confirmation of the move, reported last week by U.S. State Department officials in Washington.

  DIPLOMAT RIPPED

  ''No nation, no matter how powerful, has the right to organize, finance and serve as a central barracks for subverting the constitutional order and violating the law by conspiring, threatening security and destroying the independence of another country,'' said the Cuban government statement.

  Cuban officials have reacted strongly to what they consider unprecedented actions by Cason, the chief of the U.S. Interests Section in Havana, and have threatened to close the agency.

  In an unusual move, the acrimonious relationship was brought into Cuban homes this week via television programs. Cuba dedicated an entire show Monday night to Cason calling his contacts with government opponents ''provocative'' and ``offensive.''

  The issue was discussed again Tuesday night on Cubavision.

  'RUDE BEHAVIOR'

  Cason, who took the post six months ago, has drawn criticism from Cuban officials in recent months over his public relationship with dissidents on the island.

  ''He has traveled the island, meeting with dissidents and repeatedly showing rude behavior,'' government intelligence analyst Manuel Hevia said of the U.S. diplomat on Monday. "His actions are provocative . . . and his language offensive.''

  Hevia and other analysts on the nightly talk show Mesa Redonda (Round Table) said Cason's actions appeared to be part of a campaign to strengthen Castro's opponents. They accused Cason of meeting with ''paid agents'' and ''Cuban traitors'' before meeting with government officials and speculated it was part of a U.S. plan to derail any chance of normalized relations.

  The government-sponsored talk show also aired clips from Cason interviews, including one in Miami where he urged dissident unity and one in Havana last month where Cason told the international media that "The Cuban government is afraid, afraid of freedom of conscience, afraid of freedom of expression, afraid of human rights.''

  The comment was made at the home of Martha Beatriz Roque, where a meeting with other dissidents was taking place.

  Cason has said he is merely trying to promote democracy and human rights in the Caribbean nation.

  Castro responded to Cason's comments during a speech March 6 before Cuba's parliament by hinting that the interests section might be shut down and adding: "Actually, Cuba is so afraid that it will calmly take all the time needed to decide on its course of action regarding this bizarre official.''

  Although Castro has threatened to close the interests section before, there have been a number of other recent developments.

  A string of diplomatic notes have been exchanged and both governments have issued formal protests that vary from U.S. dismay over the inability to import textbooks for distribution to Cuba's contempt over the treatment of five Cuban nationals convicted as spies.

  CASON DEFENDED

  The Cuban government asserts the five ''heroes'' have deliberately been subjected to cruel treatment by U.S. authorities.

  Both governments also have imposed travel restrictions against diplomats in Havana and Washington.

  While Cuba characterizes Cason's bold actions as infringements on sovereignty, the United States says Cason is being a good diplomat, and it will react if Cuba takes any action against him or the diplomatic mission.

  ''Cason is a convenient scapegoat. The charges against him are baseless,'' said Daniel Fisk, deputy assistant secretary for the Bureau of Western Hemisphere Affairs. "Unprecedented [activities] doesn't mean they're outside the bounds of diplomatic activities.''

  Material from Herald wire services was used in this report.