HAVANA, April 28 (AP)--Scattered skirmishes broke out today between Cuban rebels and Army troops after a week-end of relative calm.  Clashes occurred in Pinar del Rio Province in the west and Oriente Province in the east.

In Pinar del Rio, troops killed four rebels and captured eighteen in an action that seemed to spell the end of organized dissident activity there.  Those killed and captured apparently were remnants of an estimated fifty rebels who landed there April 12.

Dispatches from Oriente said rebels had clashed early today with troops in five villages around Alto Songo, twenty miles northeast of Santiago de Cuba.  Casualty totals were not disclosed.

Fidel Castro, Cuban insurgent leader, has asserted "rebel morale is higher than ever."  Dr. Mario Llerena, chief Castro representative abroad, reported yesterday by telegram form Caracas, Venezuela, that Senor Castro had sent this word in a special message.