Special to The New York Times

    HAVANA, Jan 12--The Government reported today the capture of three top lieutenants of the rebel leader Fidel Castro.
    At the some time, reports reached here of a rebel attack on a sugar mill in the Sierra Maestra foothills.  Twenty persons, mostly sugar mill hands, were said to have been killed.
    The Moncava Army Barracks in Santiago, capital of the eastern province of Oriente, said that Javier Pazos, Armando Hart and Antonio Buch, all important collaborators in Senor Castro's revolutionary movement were captured two days ago near Bayamo.
    The were returning to Santiago from a meeting with Senor Castro at the rebel chief's Sierra Maestra headquarters in Oriente, the Army said.  The three are being held at Moncava barracks.
    Senor Pazos, a university student 21 years old, is a son of Felipe Pazos, a former president of the Cuban National Bank, who is now in Washington as an official of the International Monetary Fund.  The younger Pazos attended a preparatory school in Washington.
    Senor Hart, a lawyer, escaped from a Havana courtroom several months ago while being tried for terrorist activities.  He has defended rebels in court.  He is the son of a Cuban Court of Appeals judge.
    Senor Buch is the son of a Santiago physician.  He is said the have been an important go-between for Senor Castro in obtaining supplies and financial support.
    The attack on the Estrada Palma sugar mill by armed rebels was reported to have taken place two days ago.  A detachment of soldiers guarding the mill beat off the attack.  In addition to the twenty persons killed, a number of soldiers and rebels were wounded, according to reports received here.
    Another report form Santiago said Castro followers stopped a train near Manzanillo in Oriente.  The forced the passengers to alight and sent the train on to Manzanillo with its crew.
    The sugar mill had started grinding cane several days ago.  The rebel attack ties in with Senor Castro's avowed effort to half sugar production, the mainstay of the Cuban economy, in Oriente Province.  This is the height of the harvesting season.  The rebels have put the torch to cane fields in various localities.
    The rebels who stopped the train told the stranded passengers to "keep off the trains," it was reported.
    Both reports lacked official confirmation.  The policy of President Fulgencio Batista's Government is to maintain almost complete silence on the rebels' activities.
    The wild country of the Sierra Maestra has been the stronghold of Senor Castro and his insurgents since Dec. 2, 1956, when Senor Castro, who had been an exile in Mexico, landed on the south coast of Oriente Province with an eighty-two-man expedition.  Today he is said to have up to 2,000 insurgents under his command.
    About 5,000 members of the armed forces are being used by the Havana Government in an effort to kill or capture Senor Castro and his followers.  The Government forces have surrounded the Sierra Maestra country for several months without any apparent progress.