Twenty-one demonstrators protesting nuclear armaments and nuclear power were arrested in front of the White House yesterday shortly after 11 of their colleagues were sentenced in D.C. Superior Court on charges stemming from a similar demonstration here last September.

The arrests came after the 21 sat down in the snow in front of the Northwest gate to the White House and ignored U.S. Park police requests to leave. Nineteen adults arrested were charged with disorderly conduct and released after posting a $10 bond, while two juveniles, were released.

Those arrested were among 150 chanting and singing demonstrators who marched to the White House from the court to protest the sentencings and show that their demonstrations would continue despite arrests, said Norma Becker, chairman of the War Resisters League, a New York-based group that organized the demonstration.

Earlier, Judge Donald S. Smith ordered the 11 protesters, who were found guilty in December of unlawful entry at the White House in September, to pay a $100 fine or spend 90 days in jail. All 11 paid the fine.

Judge Smith also sentenced each of the 11 to 180 days in jail, but suspended the jail term and placed them all on probation for two to three years.