HAVANA, April 19 (AP)--Cuban troops beat off a rebel ambush today near the town of Baire, fifty miles northeast of Santiago.  Thirteen rebels were reported killed.

The Cuban ARmy said the rebels had ambushed the Government soldiers after they overran an insurgent camp near Baire and arrested a number of rebel sympathizers.  No army casualties were reported.

In Santiago, capital of rebellious Oriente Province, thousands of Roman Catholics crowded the cathedral as Archbishop Enrique Perez Serantes said a requiem high mass for three Catholic Action leaders killed in the armed uprising in Havana April 9.

Police cars guarded the cathedral but there was no trouble.  Catholic student organizations ordered a month of mourning for the three victims and said special memorial masses would be held on the ninth of each month for one year.

HAVANA, April 19 (AP)--Four rebels were killed and several wounded in a clash with an army unit at Remedios, in Las Villas Province in Central Cuba, an army communiqué said today.