MITCH Snyder, an activist for the homeless, says the fact that millions ''across the nation are living on the streets like animals is a sin, and no one shelter will eliminate that.'' It was Mr. Snyder who ended the crisis of a 51 -day hunger strike this month only when the Reagan administration agreed to turn the Federal City College building here into a ''model'' shelter for the homeless.
Most experts on the homeless estimate their number in the United States at between 2 and 3 million. And they say it is rising despite the economic recovery.
Snyder - leader of the Community for Creative Non-Violence (CCNV), a private, nonprofit advocacy group for the homeless - told a news conference last week, shortly after ending his fast: ''The situation is critical, not just here but throughout the country.''
''The homeless issue is a national issue of importance that's wiggled its way into the Oval Office,'' he said. It also wiggled its way onto the election ballot in the nation's capital, where voters approved a measure requiring shelter for the homeless.
The dramatic Snyder hunger strike, a ''60 Minutes'' TV story on it, and the initiative here have focused national attention on the problem of the homeless just as they face the onset of cold weather, which heightens their plight.
Reports from shelters around the country indicate that the problem, once thought to be a temporary crisis resulting from the recession, is chronic. But there is some uncertainty about the number of homeless in the US.
A nationwide survey has just been completed by the National Coalition for the Homeless. ''The number of homeless has gone up; it's now between 2.5 and 3 million,'' says coalition spokesman Dan Salerno. The report, titled ''The Homeless and Economic Recovery: One Year Later,'' is based on information gathered from 72 public and private shelter agencies in 12 major cities across the country.
''In the face of 18 months of economic recovery, there have been substantial increases in homelessness in virtually every section of the US,'' says the report.
The CCNV estimates the number of homeless at 3 million, as does US Rep. Theodore Weiss (D) of New York. The House human resources subcommittee, which Mr. Weiss heads, held hearings in October on problems of the homeless. Calling the situation a crisis and an epidemic, Mr. Weiss said the US treats its stray pets better than its homeless people. He noted that none of the $8 million Congress earmarked to renovate military installations as shelters had been spent for that purpose.
US Rep. Henry Gonzales (D) of Texas puts the number of homeless at about 2 million. As chairman of the House subcommittee on housing, he has held several hearings on the homeless, one at CCNV's shelter last winter. Mr. Gonzales plans more hearings as soon as the new Congress convenes.
Last May the federal Department of Housing and Urban Development estimated the homeless population at between 250,000 and 300,000 nationwide. Public controversy over the accuracy of the report reached such a pitch that House hearings were held. It was pointed out that Health and Human Services Secretary Margaret M. Heckler had, in November 1983, estimated the number of homeless at 2 million.
Responding to Mitch Snyder's demands, Harvey Vieth, chairman of a federal task force on food and shelter, pledged the administration's support of a possible $5 million renovation of the Federal City College building. Mr. Vieth had been negotiating with Snyder along with White House chief of staff James Baker III, whose wife, Susan, had been instrumental in CCNV's original acquisition of the building as a shelter.
Vieth, credited with working tirelessly for renovating the CCNV shelter, says work has already begun on it and that the task force is negotiating on shelters in four other, unnamed cities as well as in Denver.
Mr. Salerno of the National Coalition for the Homeless says his group's report ''indicates that the federal government has got to start extending itself further to (solve) the problem of homelessness, because the homeless are not going to go away.'' He cites New York City, where the number of homeless families in welfare hotels has gone up 50 percent, from 2,000 families last year to 3,000 this year, a total of 10,000 people. The number of single, homeless New Yorkers in city shelters has gone up 30 percent, from 4,783 last year to 6,233 this year.
In Boston, according to the survey, the demand for emergency shelter has increased 50 percent since 1983. In Los Angeles, the number of homeless is estimated at between 30,000 and 50,000; in Chicago, 24,000; in Atlanta, between 3,500 and 5,000 homeless men, women, and children. In Atlanta, during Christmas week last year, 20 people froze to death on the city's streets.
Says Salerno: ''The recession two years ago is still in effect for the homeless, whose lives have not improved with the current economic recovery.'' He says that things are better economically for the rest of the population but not for the poor, now estimated at 35 million.
As Representative Gonzales points out, ''this recovery is called by economists a schizophrenic recovery, a business recovery'' that does not affect the most vulnerable in our society.
In San Diego, where a mayor's task force on the homeless has just issued a report, downtown urban renovation has also displaced some of the 2,000 to 3,000 homeless in that area.
Larry Johnson, of the task force, estimates the cost of sheltering and feeding San Diego homeless this year at $1.6 million. So far the city has received a $500,000 grant from FEMA (the Federal Emergency Management Agency), which is doling out $70 million to the National Board of Volunteer Organizations for Food and Shelter.
The San Diego report has turned up ''a more realistic view of the homeless than the general attitude around the country, which is that this is just another group of bums,'' says task force chairwoman Ruth Stewart. Between 15 and 25 percent of them are families with children, Mr. Johnson says.
In Phoenix, Ariz., ''we have many more homeless than we have shelters for,'' says anthropologist Louisa Stark, who co-chairs the Phoenix Consortium for the Homeless. Dr. Stark says that from 2,000 to 3,000 homeless overflow the shelters and many are camping out in parks or open spaces.
In Baltimore, Brendan Walsh, founder of Viva House for women and children, says the need for shelter persists in that city, where there are between 15,000 and 18,000 homeless men, women, and children. Mr. Walsh says that Mitch Snyder's fast and the President's response ''have given us a lot of hope ... for the homeless in America.''
Dr. Stark of Phoenix points to the national attention focused on the homeless by recent programs like ABC's ''Nightline'' on the CCNV and the ''60 Minutes'' profile of Snyder. ''Some of us are inspired by Mitch's selflessness,'' she says. ''It will be interesting now to see how words are transferred into actions.''