After marching under yesterday's burning sun, they walked slowly up toward the Washington Monument through an archway with posters proclaiming "O Jerusalem." More than 1,000 of them straggled in, smiling as they picked up souvenir plastic throwing discs that said "I did it!"

The second annual "Walk Celebration," sponsored by three major Washington-area Jewish organizations to raise money for Israel, had begun. By the time it was over late yesterday afternoon more than 8,000 people - estimates by festival organizers ran as high as 10,000 - had joined in the activities on the monument grounds.

The thousand who participated in the morning walkathon from the monument around the Capitol to Dupont Circle, Georgetown, the Tidal Basin and back again to the monument - 18 kilometers or 11.25 miles - were easy to spot. Some were wearing sunshades and yarmulkas, most wore stickers reading "We walk as one," and most looked dead tired.

"Well, it was hot," said a heavily perspiring Harvey Peritt of Beltsville, who marched with his wife and one of his sons. "But it was worthwhile; what you call a mitzvah in Hebrew, a good deed for charity."

According to festival organizers the walkathon raised $50,000, which will be sent to Israel to aid in humanitarian programs, including tuition for impoverished children, medical care for the aged and resettlement programs for Soviet immigrants.

The afternoon's activities, and the crowd itself, were a demonstration of the diversity of Jewish culture, the vast numbers and kinds of people who share the Hebrew faith.

Music ranged from traditional to a kind of Hebrew hootenanny played by a group called Gush Egozan (glob of peanut butter), mingling Jewish and bluegrass themes.

Jews who recently came to the United States from the Soviet Union, from Morocco and Iran were on hand to celebrate the 31st anniversary of Isreal's independence.

One young Persian Jew said that although his family was never persecuted officially by the new Islamic regime in Tehran, several friends had received threats and anonymous notes. "There was the rumor," he said, "that you have to leave everything and leave the country." He had.

As keynote speaker Rep. Robert Drinan (D-Mass.) spoke of "the dream of 'next year in Jerusalem'" that is the heart of Zionism and declared that the holy city "must always remain . . .the capital of Israel." He received a standing ovation in front of the monument ground's Sylvan theater, before, once again, the crowd turned to the sheer, if steamy, pleaures of the scene. CAPTION: Picture, Jewish folk dances by The Heritage Dance Group were included in Sunday's event. By Margaret Thomas - The Washington Post