BERLIN (AP) _ A bomb exploded early Saturday in a crowded night club frequented by U.S. soldiers, killing two people and injuring up to 150 others, police said. The Pentagon said at least 30 Americans were hospitalized.

Police said a man and a woman were killed when the blast devastated the La Belle discotheque in the American sector of the divided German city at 1:50 a.m. (6:50 p.m. EST Friday).

Their nationalities were not immediately available, but State Department spokesman Ed Harper in West Berlin said ''there is good reason to believe at least one was an American.''

At least 30 people wounded in the explosion were in serious condition, police said.

A statement released by the U.S. military in West Berlin said only that an explosion had taken place and that ''there appeared to be a number of fatalities.''

In Washington, a Defense Department spokesman said ''six to nine Americans were seriously injured and 30 to 35 required hospitalization.''

''An unknown number are receiving medical treatment and did not require hospitalization,'' said the spokesman, Lt. Cmdr. Ross Kudlick.

Kudlick said the department has not been able to confirm whether the Americans were U.S. servicemen, but said he believes ''some percentage will be U.S. service members.''

In Santa Barbara, Calif., White House spokesman Peter Roussel said President Reagan, vacationing at his nearby ranch, was notified of the blast at about 8 p.m. PST (11 p.m. EST) by Donald Fortier, an official of the National Security Council, who accompanied the president to California.

''We have received reports that a number of people have been injured, including some Americans and apparently there have been some fatalities, but we have no details,'' Roussel said.

Sgt. Donald Banks, a military spokesman in West Berlin, confirmed the discotheque was a popular spot with West Berlin-based Americans, but declined to say whether U.S. soldiers or dependents were among those injured.

''You can deduct that, sure,'' he said. ''But there is no official word yet and they are investigating it right now.''

At least 500 people were in the night spot at the time of the blast, a police spokesman said.

The Berlin political police took charge of the investigation.

More than 6,000 U.S. soldiers are stationed in West Berlin, and a police official said investigators were not ruling out a political motive for the attack.

The official, who refused to be further identified citing police policy, said no claim of responsiblity had been received.

The U.S. troops belong to several units, including the 4th, 5th and 6th battalions of the 502nd Infantry Regiment.

West Berlin is more than 100 miles inside communist East Germany, and is administered by the United States, Britain and France under a World War II agreement.

The powerful blast caused a partial collapse of the ceiling and buckled walls in the ground-floor night spot. Witnesses said a small fire broke out after the explosion, but was quickly extinguished.

The blast shattered the nightclub's mostly glass front and blew out windows in surrounding stores. Scaffolding set up along the front of the five-story building in which the club was located buckled, but did not collapse.

Hours after the explosion, some 100 West German and U.S. military police were at the roped-off site examining debris and holding back early-morning spectators.

In the last attack involving U.S. soldiers in West Berlin, an anarchist group blocked a U.S. military train traveling into the city in November 1984 by piling tires and oil-filled canisters across the tracks and setting fire to them. No injuries were reported.

According to West Berlin statistics, 37 arson and bomb attacks took place in the city in 1985.