"Loneliness." Msgr. John J. Murphy was saying as he surveyed the crowd surging past him, "is a form of poverty in way."

Resplendent in his purple robes. Murphy stood next to Cardinal William Baum, archbishop of Washington, greeting guests from the Washington area who had come for the National Shrine of the Immaculate Conception's third annual Christmas Day Dinner in the Shrine's cafeteria.

More than 600 persons came on a sunny, warm Christmas Day to have a free meal of turkey, mashed potatoes, peas, cranberry sauce and dessert.Many of them were personally welcomed by Baum and Murphy as they cutered the cafeteria atter the noon Christmas mass celebrated by Baum.

The idea, according to Baum, started two years ago "because of the stories we heard about people who didn't have families. You know, Christmas can be a difficult time. This seemed to us to be a good way to celebrate Christmas."

Dorothy West, a resident of Southeast Washington, sat at a table with here two sons, Brian, 9, and Laron, 2. She said she had read in the paper about the Christmas dinner. She came on the bus with with her sons because "We had nothing to eat." West said she works for ACTION and "I get paid tomorrow."

In the meantime, Brian, speaking for the family, said everything was "fine."

Gertrude Maye Sterns brought her three daughters - Patricia, 8, Jackie, 7, and Kimberly, 20 months-and her son, Matthew, 3. She said she had been invited several months ago by a nun in Northeast Washington to come to the dinner. "it beats being alone," she said. She hesitated for a moment, looking at her children cramming food into their mouths. "I don't know," she added. "It's better for them."

Waiting to serve the persons who came, or who were brought to the Shrine, were about 135 volunteers-including many non-Catholics-who found the dinner a fitting way to celebrate Christmas.

Patty Kane, 21, a puppeteer and sometime student at the University of Maryland, said that at Christmas she usually plays Santa Claus for retarded persons at Great Oaks, but that this year she came back to Washington too late to do that.

Kane said she makes a point of volunteering. "You meet a lot of nice people," she said. "I'm always volunteering-one thing or another always comes up. If you volunteer all the time, you learn a lot from it, you really do. People who volunteer get things back. You make the world a little bit more the way it should be."

The volunteers quickly and cheerfully took orders from the guests and carried trays of food from the cafeteria line back to the tables where they were seated. Other volunteers cleared tables, served food and washed.

"I guess the real truth of the matter is I don't do vvery much for anybody during the year but myself," said Joe Coudon, 35, an administrator for the Federal Judicial Center, in explaining why he had volunteered. "This is an opportunity for me to do something for someone else and Christmas is a good time to do it."

Although some who came were poor, the idea of the dinner, as Murphy and Baum explained it, was to give people who were alone or who had no place else to go a place to come for Christma.

"It's really a family thing." Murphy said several times, emphasizing the pains that were taken to make people who came feel that they were wanted. An effort was made to keep the guests from standing in line for an extended period of time. "People tell us when they leave that their dignity is maintained." Murphy said.

"A lot of these people don't know each orther." Murphy said, "but they are sitting here like family"

The Marriott Corporation, which operates the cafeteria for the Shrine, donated about 1,000 meals. Eight of the cafeteria's regular employes, including the manager, Timothy Jones, donated their time yesterday, along with two vice presidents of Marriott, three other company executives and two of their wives.

For the volunteers, Murphy said, the dinner "fulfills a terrific need for people who want to do something Christmas Day because it's in spirit with the day."

Charles Mills, a Baptist who is vice president of Marriott and who stood over the cafeteria steam table dishing out turkey and mashed potatoes, said the dinner "gives the folks something other to do than worry about what they got for Christmas."

William A. Grillo, the assistant director of the Shrine, was eating his own dinner with the volunteers after all the guests had been served, when one of the volunteers approached to say that she was leaving. She thanked Grillo for letting her work this year. "I hope 1979 is good to both of you," she said to Grillo and his companion. "See you here next year." CAPTION: Picture 1,2, Jill Moscowitz (left backround) plays the guitar and sings at a Hanukah Celebration at The Jewish Community yesterday. At right, Spec, 4 Larry Leonard stands a tour of duty at Tomb of the Unknown Soldier. Photos by Gerald Martineau-The Washington Post