Ground Zero Week, the nationwide project designed to educate the public about the perils of nuclear war, ended here last night with an observance as low-key as most of the events it sponsored--a candlelight rally across from the White House in Lafayette Square.

The seven days of town meetings and seminars highlighting the nuclear specter were not particularly well attended in this area, but organizers of the project said last night that they were heartened by the response elsewhere in the country. They said that Ground Zero-sponsored meetings, seminars and demonstrations were held in about 600 cities and 300 college campuses around the country and estimated that more than a million people attended at least one such event.

"We weren't flashy, but we got people talking to people about the dangers of nuclear war," Ground Zero organizer and national director Roger C. Molander said at last night's rally. "We are just extraordinarily pleased."

Among featured speakers at the observance were Sens. Gary Hart (D-Colo.), and David F. Durenberger (R-Minn.), and D.C. City Council member Hilda Mason (Statehood-At Large), honorary chairman of Ground Zero in Washington.

"We will be destroyed by the preparations for nuclear war," Mason said in apparent reference to massive allocations for defense by the Reagan administration. "Let's spend money to sustain life on this planet, not destroy it."

Hart told the gathering of about 400 that children today have stopped asking "What did you do in the war, daddy?" and are asking, instead, "What did you do to stop the war?." He called upon the audience to help him persuade his colleagues in Congress to limit production of nuclear weapons.

"Nuclear war means oblivion," Durenberger said. "It means the end of spring, the end of watching a child grow."

Molander, a former arms-control specialist with the National Security Council, said he hopes the lessons of Ground Zero Week will serve as a springboard for another round of nonpartisan consciousness-raising sessions on nuclear arms planned to coincide with congressional reelection campaigns around the country.

The impetus for the Ground Zero movement, Molander said, was the need he and other organizers felt to make understandable to average Americans the complex issue of nuclear arms control and the consequences of atomic warfare.

Just before darkness fell last night, a runner from American University, escorted by a score of others, arrived bearing a torch fashinoned from an emergency flare from which members of the audience lit their candles. The crowd then walked across the street to the White House gate where they sang--among other protest songs reminiscent of the 1960s--"We Shall Overcome" and "Where Have All the Flowers Gone?