MIAMI, Feb. 4 (AP)--The indictment of thirty persons on charges of conspiracy to undertake a military expedition against President Fulgencio Batista was announced today.

United States Attorney James Guilmartin said they probably would be arraigned Feb. 17.

They were arrested at a dock at Big Pine Key, south of here, Nov. 19 and were released on bail.

Most of them are Cubans.  Some claim United States citizenship.  They were described as sympathizers with Fidel Castro, leader of a band of anti-Batista rebels who make their headquarters in the mountains of Cuba's Oriente Province.

The Federal grand jury also charged those arrested with conspiracy to export United States arms, ammunition and "instruments of war" to Cuba.

With the arrests, immigration and customs officers seized a Diesel cruiser, the Philomar III.  Loaded with arms and medical supplies, the boat was being prepared for a dawn sailing.

The grand jury said that for several days before Nov. 19, the defendants had been assembling rifles, machine guns and miscellaneous equipment and loading it on the cruiser.

Each of the offenses charged is punishable by up to five years' imprisonment.

Special to The New York Times.

HAVANA, Feb. 4--Rebels in Oriente Province led by Senor Castro increased their activities in the last few days in and near their Sierra Maestra stronghold.

Twelve bombs exploded tonight in Havana and its suburbs, causing no injuries.  Entrances and show windows of commercial firms were destroyed.

One soldier was killed and two were wounded in an encounter with eighty rebels at Yara Arriba.  The rebels robbed a general store there of $8,000 worth of food and clothing, according to the authorities.  Five civilians died in the attack, including Oscar Arias, owner of the store.

A group of rebels assaulted a lighthouse at Cabo Cruz, on the southwest tip of Oriente Province.  All supplies there, including some dynamite, were carried off.  One sailor was taken prisoner.

Rebels blew up a locomotive belonging to the San Ramon sugar mill.

Late yesterday a small plane flew over cane plantations of the Resuelta sugar mill at Sagua la Grande, on the north coast of Las Villas Province, and threw out tubes of phosphorus.  Fires started immediately.  A hundred thousand arrobas, containing twenty-five pounds of cane each, burned, the report said.

Juanita Castro, sister of Senor Castro, arrived in Havana tonight by ferryboat from Key West, Fla.

[She slipped into the United States form Mexico last month and was ordered deported.]