It was a seemingly shy Bernice King who stepped onto the podium yesterday at a mid-day ceremony honoring her father, Martin Luther King Jr., who would have been 56 today.

But once the 21-year-old woman opened her mouth to speak, the shy image was shattered. "Today, patriotism is high, but compassion is low," she said. "The real threat in America today is not from without but from within. The real power of America is in its people, not in its ability to exert power."

During the 15-minute speech to more than 1,000 people who packed the auditorium of the Department of Health and Human Services, King quoted her father, criticized President Reagan's budget cuts and implored those attending to help their neighbors.

Her voice was strong and her words bold. Those who wanted to see in Martin Luther King's youngest daughter reminders of the late civil rights leader were not disappointed. At times during the speech, King sounded like a preacher. Both her cadence and prose were reminiscent of her father's oratory.

After criticizing budget cuts that she said had jeopardized some social programs for the poor and elderly, King said, "Middle-class Americans must realize: While we may have come over on different ships, we are all in the same boat now."

"You are definitely your father's daughter," moderator Jane E. Branche said to King afterward, as a few people shouted, "Amen!"

King's speech, "An Infinite Light in a Finite World," was interrupted several times by loud applause from the audience, composed mostly of government workers.

The commemoration, one of several held by various government agencies yesterday, also featured inspirational and gospel songs by the Northeastern Presbyterian Church Chancel Choir and the Michael McNeill Singers.

King, a senior and psychology major at Spelman College in Atlanta, plans to attend law school and eventually earn a PhD in philosophy, religion, political science or psychology. She was 5 years old when her father was assassinated and has said that many of her memories of him are not vivid.

The only personal recollection she offered yesterday was of her father asking a saxophonist to play "Precious Lord" one evening when he was to speak. The speech was the last he made.

"They may have slayed the dreamer, but the dream lives on," King told her audience yesterday. "Even in death, I believe he is shining brighter than he ever did in life."