Every morning when Harold Moss leaves the relative security of his small room in a downtown Washington shelter, he is assailed by the poverty in which he has chosen to live. As shelter director, Moss is accustomed to food scrounged from dumpsters, to rats and roaches, to the stench of human waste, and to sharing the only working shower with 600 homeless men.

A devout Catholic obsessed with serving the poor like his hero St. Francis, Moss, 43, has made extraordinary sacrifices.

He left a promising career as a cancer researcher, a 10-year marriage and a comfortable home in suburban Maryland to join Washington's Community for Creative Non-Violence. Since then he has endured a winter living on a heating grate, a summer fasting, more than 60 days in jail for acts of civil disobedience and the despair of elderly parents who do not understand why eight years ago he threw away a life it took generations of blacks to attain.

Sometimes he wonders, too. "I can't burn out, believe me I would love to," said Moss, a wiry, intense man. "The goals of this community, not the individual, are the most important thing. Together we can accomplish a lot, but it's a constant daily struggle to live like this."

His struggle is shared by an unlikely group of four dozen teen-age college dropouts, middle-aged ex-convicts, radical Catholics and former alcoholic street people who have little in common except a shared vision and the ability to translate into action their twin goals of serving the poor and eliminating homelessness.

Operating out of a decaying nine-bedroom Victorian house in a ghetto neighborhood, this ragtag group has been a major factor in thrusting homelessness onto the national agenda. By combining the tactics of civil disobedience, a flair for guerrilla theater and a shrewd sense of timing and targets, the CCNV has forced President Reagan, Congress and a score of public officials to respond to the homelessness issue even as the moralistic rhetoric espoused by Mitch Snyder, its best-known member, has alienated its natural allies.

The 41-year-old Snyder, bedridden and critically ill, yesterday completed the 50th day of a hunger strike designed to force the administration to improve conditions at CCNV's shelter, one of the nation's largest.

"There's a real love-hate feeling about them," said Keary Kincannon, until recently director of the Coalition for the Homeless, a group that opposes a CCNV-sponsored referendum. "They've probably done more than any group in the U.S. to raise the national consciousness about homelessness, but there's a real strong distaste for the way they make decisions without consulting anybody."

Led by Snyder, a complicated, charismatic convicted car thief influenced by radical priests Daniel and Philip Berrigan, CCNV has scored an impressive string of victories.

Last spring the group convinced District election officials to adopt new regulations to permit the homeless to vote -- the first in the country -- and these were quickly copied by New York City. It was CCNV that gathered 32,000 signatures, defeated court challenges and succeeded in placing on Tuesday's D.C. ballot the first referendum that would guarantee overnight shelter. In March, after federal officials vowed to evict the homeless from the squalid shelter at 425 Second St. NW, Snyder threatened to organize a march on the White House. President Reagan then ordered the 800-bed facility to remain open indefinitely.

Most recently, CCNV has attracted international attention by erecting "Reaganville," a tent city in Lafayette Park across from the White House and demonstrating against the administration's policies. More than 200 activists, among them pediatrician Benjamin Spock, have been arrested for acts of civil disobedience ranging from praying on the White House lawn to releasing 100 cockroaches -- trapped one midnight in the kitchen of CCNV's communal house -- in the State Dining Room.

It is CCNV's work with the poor, not its penchant for theatrical nonviolence, that has attracted the attention of an unlikely group of supporters. Susan Baker, wife of the White House chief of staff James A. Baker III, interceded last winter to help CCNV obtain for $1 an abandoned federal building three blocks from the Capitol for a shelter. Barbara Bush, wife of the vice president, hosted a tea for CCNV members and cabinet wives at her residence and made two trips by official limousine to drop off clothing at CCNV's headquarters and communal house at 1345 Euclid St. NW.

The "roach action," as it was called, reflects one of the gritty realities of life at "1345," where an atmosphere of purposeful and at times barely controlled chaos prevails.

The house is decorated with wrinkled political posters and stained, mismatched furniture. Its most distinctive features are the pervasive smell of 30 stray cats and the six rectangular Lucite boxes atop a battered white piano in the living room. Each contains the ashes of a street person who froze to death.

Seventeen members live there, including the trio of leaders: Snyder, chief spokesman and theoretician; Carol Fennelly, the 35-year-old organizer, and Mary Ellen Hombs, 33, the ethereal-looking daughter of a retired Air Force general.

Hombs, the senior member, joined CCNV 12 years ago and handles the annual budget of about $120,000. CCNV raises money through periodic fund-raising letters, each personally signed and sent to 10,000 names on its mailing list. The group has rejected seeking nonprofit, tax-exempt status, fearing it would impose untenable political restrictions.

Six other members live and work across the street at a 17-bed infirmary for the homeless opened last year after "1345" could no longer accommodate the 40 street people -- many of them with medical problems -- who were routinely sleeping on the first floor and sharing the two bathrooms. About two dozen other community members, half of them former street people, live and work at the shelter.

At 1345, eight telephones -- three incoming lines and three outgoing -- ring incessantly, and people run in and out ferrying more than a ton of food a week bound for the soup kitchen or food store. Dinner is at 7, and the cook of the day must figure out how to combine whatever has been scrounged from dumpsters at wholesale markets or donated from a local Giant Food store. One recent dinner consisted of boiled cabbage, baked potatoes and cottage cheese.

Few people have their own bedrooms. Some sleep on discarded mattresses in closets that are chilly in winter because CCNV, three months behind on the $850 rent, cannot afford heat.

Drugs, alcohol and promiscuity are all discouraged, and most private property is shared. At times the differences in background, grueling work, lack of sleep, bad food and resentment about Snyder's special status infuse communal life with all the tensions of a bad marriage.

The chief virtue is not self-awareness but self-denial achieved through a combination of Christian spirituality, hard work and fasting.

"This is a place that is very radical, that demands of people that they go beyond where they think they can," said Fennelly, who left a life as a suburban California housewife a decade ago to take her two small children east in search of "a living gospel."

"It's a very intense place in terms of relationships, workload, mission and vision because of the proximity with which we live our lives to the people we serve," said Fennelly, who has seen 100 people leave CCNV, many of them victims of burn-out. "We're not these nice little middle-class advocates who go home at night. We bring the presence of the poor with us because we are poor, but I have no illusions. I could walk out of here tomorrow, but my next door neighbor can't."

That sense of rage and the excitement of living on the edge has distinguished CCNV since 1971 when it was founded by four Catholic antiwar activists at George Washington University.

"From the beginning, CCNV was always to the left of everybody," recalled founder Ed Guinan, a former priest no longer affiliated with CCNV. "We were never willing to play the game where everybody's board was satisfied."

When the Vietnam War ended, CCNV, then located in a house on Washington Circle, shifted its focus. It founded the city's first free medical clinic, a shelter then called a "hospitality house" and a soup kitchen.

"What has changed is the social topography," said Guinan. "People in the early 1970s were not aware of hunger and homelessness. They just refused to believe there were people sleeping in cars."

For the past decade the dominant -- and many say domineering -- force in the community has been Snyder.

He is regarded as both its greatest asset and its chief liability, a man charismatic enough to attract scores of eager new members, shrewd enough to force politicians to respond to his agenda and savvy enough to move in the disparate worlds of tea at the vice president's house and dinner at the soup kitchen.

"Mitch is the homeless guru, and people support the guru," said Audrey Rowe, the District's commissioner of social services. "He's committed, he's passionate, he's very personable and he's a very good PR man. Homelessness is an issue people see every day. It's fairly easy to get them to want to do something about it."

Last year, however, Rowe was so offended by Snyder's strident accusations that she refused to appear in the same television studio.

Snyder, an articulate and iconoclastic high school drop-out who calls his Jewish mother in Brooklyn every week, displays an imperiousness that often angers CCNV members, even as they admire his gifts. "He talks about all this service work we do but he never does it unless there's a TV crew along," one said.

Snyder acknowledges that is true but says he makes other contributions.

"I bring out a lot of good in people," he said recently, "but I ain't Mother Teresa." He describes himself as a "very selfish, very controlling, pigheaded person with a fanatical belief in the supremacy of goodness."

Those qualities were apparent in 1978 when CCNV became embroiled in a bitter battle with Georgetown's Holy Trinity Church, a wealthy, liberal parish whose members include the Kennedy family.

After demanding that the church use some of its $400,000 building fund to help the poor, Snyder began a hunger strike. A psychiatrist tried to have him committed, the church flatly rejected his demands and Snyder, hospitalized near death, ended his fast.

"It became a personality thing," said Guinan. "The lesson was that you can't destroy your base as you're trying to build it."

Four years later CCNV used a very different strategy and the result was the nation's model food reclamation program.

In 1982 CCNV received national acclaim after serving a meal of crabmeat quiche and fresh boysenberry shortcake to 30 congressmen. The meal was made from food scrounged from supermarket dumpsters.

At the time CCNV was trying to persuade Giant Food, a local supermarket chain with a liberal reputaton, to give away thousands of pounds of routinely discarded edible, but unsaleable, produce and baked goods.

CCNV picketed supermarkets and held sit-ins in dumpsters. When Giant started locking the dumpsters, claiming the food was unsafe, CCNV dispatched 28 members -- exactly the number of seats in the waiting room of Giant's corporate headquarters -- to meet with officials.

Giant refused the meeting and had protesters arrested when they refused to leave.

Several weeks later, during a radio show, Snyder suggested to Giant spokesman Barry Scher that the food be given to the Capital Area Community Food Bank, not CCNV, to distribute.

Giant agreed and the program became a national prototype. Giant earned corporate kudos, and every month more than 50,000 pounds of food that had once been discarded feeds the hungry.

"A very bad situation initially turned into a very positive program for Giant," said Scher. "We owe it to Mitch and his people for making us see the light. Even though they were difficult to work with, they did have some good suggestions."

"They really did our dirty work," said food bank director Rick Stack. "We were trying to mildly cajole Giant , whereas CCNV's style was much more aggressive."

Strategy and tactics -- whether to release cockroaches or begin a public fast -- are hashed out at frequent meetings. It took months to decide whether to get more than one phone line, but a decision about who can become a member is an uncomplicated process requiring a consensus.

At one recent session members agreed that although the "roach action" might anger some people, it was humorous and not as alienating as blood-pouring. Most importantly it was a graphic reminder that only cockroaches might survive a nuclear war.

Often the focus is more mundane: how to clean the wok, whether the tangerine mesh curtains should go to a men's dorm known as "the swamp."

"Living in community is a lot like being married, except to 15 different people," Fennelly observed. "People come in with all sorts of idealistic notions just like when you first fall in love. In order to stay here, you have to shed those notions and fall in love a second time. Reality sets in when you start living with people and see how they squeeze the toothpaste."

Sometimes she wonders what impact her life style has on her teen-aged children, both of whom yearn to be middle class and live alone. She regards their aspirations -- her daughter wanted to join ROTC, her son is a breakdancer -- with the same baffled disapproval with which her Orange County Republican parents view her "downward mobility."

"There are times when I'd give my eyeteeth to be a normal person and live in a house alone with my kids, but I can't do that," she said. "Mitch and I have never had a normal male-female relationship." Last summer they took a Reaganville tent to Chincoteague to camp, their first night alone in five years. "It was really strange," she recalled. "Even then someone recognized Mitch."

Nevertheless, Fennelly, who left CCNV for a year to work with the poor in Los Angeles, fervently believes in what she is doing.

"As individuals, we could not do anything," she said. "We are a moment in time, we're doing a task and paying a very high price for it. God has called us together and we're burning the candle at both ends. But while we're burning we're going to shed a lot of light where there isn't any.