Tens of thousands are expected to gather Saturday at the Lincoln Memorial to commemorate Rev. Martin Luther King Jr.'s "I Have a Dream" speech of Aug. 28, 1963. Organizers hope to rekindle that dream, which he shared with the nation 25 years ago during the march on Washington. King's widow, Coretta Scott King, Democratic presidential nominee Michael S. Dukakis and civil rights leader Jesse Jackson will address the gathering. Vice President George Bush did not respond to an invitation, said the Rev. Joseph Lowery, who succeeded King as head of the Southern Christian Leadership Conference. An estimated 250,000 people marched in Washington on Aug. 28, 1963, a great day in the civil rights movement. The same number of people commemorated the 20th anniversary of the march. Lowery said he expects "throngs" to march Saturday. The march in 1963 spurred Congress to pass the Civil Rights Act of 1964. Since 1963, said Lowery, "everything has changed and nothing has changed."