On the eve of their four-day Christmas holiday, several thousand State Department employes marched solemnly yesterday to the Lincoln Memorial to ask that their 50 captive colleagues be freed by Iranian militants.

There, they were joined by other federal workers, many with tears in their eyes, and the crowd of about 7,000 listened as a message from the top U.S. official in Tehran was read. They also joined in singing songs that he had requested for the brief ceremony.

They stood silently in chilly, 39-degree weather and watched sunny skies turn gray as the somber ceremony progressed.

As the emotional gathering drew to a close, Marine Corps soloist Michael S. Ryan sang the American slave spiritual, "Let My People Go," in a loud clear voice.

"Go down, Moses, way down in Egypt land. Tell ole Pharaoh, let my people go."

The poignant song had been requested by Bruce Laingen, the charge d'affaires at the U.S. Embassy in Iran, who was away from the embassy when it was stormed, but has been held in custody by the Iranians.

At the request of laingen, who is in telephone contact with the State Department, the crowd also sang "God Bless America," and "The Battle Hymn of the Republic", and the Marine Band played "O Come All Ye Faithful" during a silent prayer.

"We salute you and we join with you in this demonstration of unity and support of those who represent us in silent dignity at our embassy in Tehran," Laingen said in a brief message that was read to the crowd by Harry G. Barnes, Jr., director general of the foreign service.

Laingen's wife Penne stood nearby as did Gay Vance, wife of Secretary of State Cyrus Vance. Relatives of hostages were sprinkled throughout the memorial in front of the half-frozen Reflecting Pool.

Laingen said he, the hostages and those gathered for the demonstration all prayed "that good will and the spirit of justice will guide us, Americans and Iranians alike, toward a prompt and peaceful resolution of this crisis in a way that will be worthy of these two great nations."

Co-workers helped Janet Henneke, 30, a State Department economics analyst, carry a huge sign reminding people to write letters to the Iranian Embassy, urging that the hostages be freed.

"People may be tired of writing but they [the hostages] are tired of being there, too," she said.

The organizers of the ceremony were pleased by the size of the turnout.

"I was afraid, because of the Christmas season with people so busy that we wouldn't have much of a crowd," said Frank Matthews, head of the public affairs office for the foreign service. "But this is super."

One man in the crowd recalled that exactly one year ago he had attended the Christmas party at the U.S. embassy in Tehran.

The theme of the march -- "Let Our People Go" -- was sounded at the beginning during a brief ceremony in front of the State Department.

Alan K. Campbell, head of the Office of Personnel Management, presented Barnes with a 25-foot-long petition, signed by an estimated 3,000 federal government employes, that urged the Iranian government to free the hostages.

"This petition is more than a list of names," Campbell said. ["It shows] that the people of the United States are one . . . Our message is simple and firm . . . that our fellow workers be allowed immediately to come home."