The National Christmas Tree's 1,200 lights -- and some other luminaries -- drew 12,500 visitors to the Ellipse last night for the annual lighting ceremony.

Just before 6 p.m., President Reagan flipped a switch in the White House and the 30-foot Colorado Blue Spruce was bathed in red and gold. The lights are brighter than ever, according to the U.S. Park Service, and slowly change to all red.

Also wearing all red was Willard Scott, the weatherman of the NBC "Today" television show, who played Santa Claus.

Joining Scott were two vacationing Floridians, Mickey and Minnie Mouse, and the Voices of Liberty singers from Disney World. Bands, including the Air Force Band, played Christmas music, accompanied by the chattering teeth of some onlookers.

In keeping with Christmas music traditions, Jack Frost was nipping at the noses of folks dressed up like Eskimos, and many tiny tots with their eyes all aglow were held aloft by well-bundled arms as they stood together in chilly 50 degree temperatures.

Singer Tony Bennett sang the Christmas classic "Santa Claus Is Coming to Town" with his daughters Joanna and Antonia.

The crowd watched the Reagans on a large video screen. Mrs. Reagan, dressed in red, held the First Family's new dog, Rex.

The president said in a brief speech that "no prisons, no walls, no boundaries can separate the members of God's family." He added that "greater than all mankind's military might is . . . godly love."

The Christmas Pageant of Peace will be on the Ellipse until Jan. 1. There will be music nightly and nine reindeer from the National Zoo are spending the season on the Mall. That is, every night except Christmas Eve.