BERLIN, April 15--Communist East Germany dimmed hopes today for East-West agreement at next month's foreign ministers conference.

Premier Otto Grotewohl, in a belligerent speech before East Germany's Parliament, outlined an uncompromising policy that undoubtedly foreshadowed the stand Soviet Foreign Minister Andrei Gromyko will take at Geneva May 11.

Geneva prospects also were darkened by another exchange of Soviet and U.S. protests over the latest buzzing of a high-flying American transport plane by Soviet MIG jets on a flight to Berlin.

In his speech Grotewohl declared: "The question of reunification is an internal German affair and will not be a matter for debate at Geneva."

Cubans Hijack Airliner

MIAMI, Fla, April 16--Taking a cue from Fidel Castro's revolutionary script, four of his enemies hijacked a Cuban domestic airliner today and forced its pilot to fly them to Miami in search of political asylum.

Nineteen passengers, including five Americans, and three crewmen stepped out unharmed when the twin-engine C-46 landed at Miami International Airport. The hijackers were grabbed by U.S. border patrolmen.

Three of the gunmen claimed to have escaped from Havana's La Cabana Fortress while under threat of execution.

Montana Prisoners Riot

DEER LODGE, Mont., April 16--Rioting Montana convicts armed with knives and guns, shot and killed a deputy warden today and grabbed 19 hostages including Warden Floyd E. Powell.

Powell was released unharmed about two hours later, apparently as the result of an ultimatium by Gov. J. Hugo Aronson. The 18 others, all guards and prison employes, remained prisoners of the shouting inmates.