The Cuban Government said today that a United States-made B-26 bomber that came from the north and ''retired with a northern heading" staged a raid on sugar-producing Pinar del Rio Province Sunday. But it implied that the attack had been fruitless.

The plane dropped a 250-pound bomb over the patio of the home of' a peasant, Domingo Brach Banos, near the town of Consolacion del Norte, said a communique issued by the Armed Forces Ministry. The communique thus confirmed a report by Cuban exile sources in Miami that there I had been such a raid.

The exiles told a Miami news conference that the plane had dropped incendiary and high explosive bombs on the Niagara sugar mill and on cane fields.

The communique indirectly denied the details saying: "In Miami, a counter-revolutionary organization stated that it made this cowardly attack on the Niagara sugar mill, which is situated nine miles from where the bomb was dropped."