NEW YORK — "WE pay cash for your guns - no questions asked."That's the message from a growing number of urban police departments these days. San Francisco and St. Louis have just completed experimental gun buy-back programs. Brooklyn, N.Y., has taken in 500 guns since it began a program Nov. 25. Rochester, N.Y., began a similar program this week, and Atlanta is scouting out potential corporate donors. The spur for such programs often comes from local political leaders. They are under strong pressure to do more to curb rising crime. In paying cash for guns, they hope to cut down on the growing number in circulation that could be used in family fights or used in violent crimes. New York City Police Commissioner Lee Brown, a partner in the Brooklyn program started by District Attorney Charles Hynes, says that saving even one life is worth the effort. Police departments have tried gun buy-backs on and off over the last two decades. The fresh steam now may be partly due to what Gwen Fitzgerland, spokeswoman for Handgun Control Inc. calls the rising level of citizen frustration with Congress's failure to act on tougher gun control measures such as the Brady bill. "People want to do something," she says. "More guns do not make us safer, so I think it follows that fewer guns is going to help." Still, critics say that with an estimated 200 million guns circulating in this country, the impact of such programs is slight. It is a symbolic public relations effort, they say, that will never persuade criminals to turn in usable guns. "Law abiding citizens are turning in guns that they ... haven't any use for - a lot are pieces of junk," says National Rifle Association spokesman Bill McIntyre. "I really don't see this as having any crime-reduction value, but it apparently leaves a warm, fuzzy feeling with some folks." "Some people argue that the hard-core criminal will always have a gun...," says Tom Reppeto, president of the Citizens Crime Commission of New York City. "That's true. However, there are a lot of people around who are not criminals on a regular basis but get angry in fights and get guns. If those guns weren't around, maybe a life could be saved." Police say that only functioning guns are accepted and that the number seized is not the only measure of success. "I think we're trying to send a message saying that we're taking the [gun and crime] problem seriously...," says Pamela Bellomio, an employee of the Rochester police department. "We think there's a lot of citizen support for this kind of program," agrees Lt. Lou Arcangeli of the Atlanta police force, "and we want folks who are civic- minded to come forward and help us with it." Buy-back proposals net particularly strong public support if they are part of a broad crime-fighting program and are started by a community-based organization, says James Mills, executive director the Philadelphia Anti-Drug and Anti-Violence Network. That group launched a two-week gun buy-back last summer that collected 1,044 guns. "The program sent a message of hope throughout the city that we can do something about the problem if we all come together," says Mr. Mills. "Before, there was a sense of 'Well, you can't really do anything.... The money for gun buy-backs often comes from assets confiscated from drug dealers and from private funding sources. Yet setting the price at a point which does not create a market for guns is a delicate chore. Both San Francisco and St. Louis, which collected an impressive 7,469 guns in its one-month program last fall, paid $50 per handgun, a price some consider too high. The Brooklyn program has paid as much as $75 per gun. Philadelphia paid a low, flat rate of $20 each. Mr. Mills calls it an incentive rather than a buy-back. "If you ask citizens to turn in their guns to make the neighborhood safe - and as a byproduct give them a $20 bounty," he says, "you do more to involve and empower community people." Many police departments, including New York City's, have tried straight gun amnesty programs with varying success. An amnesty offered in October by the District of Columbia, the nation's number one city in homicides on a per capita basis, drew 200 guns among an estimated 600,000 in circulation. The guns are to be melted down for manhole covers. Boston, which ran a similar amnesty program through the churches for one week last summer, collected 14 guns. Several cities which have tried the gun buy-backs say they would do it again if they had the funds. "Our program was successful - we just ran out of money," says San Francisco police department spokesman Jerry Senkir. The National Rifle Association's Bill McIntyre says that he is amazed that any money could have been spared for such programs during a recession. The money would be far better spent, he says, in reforming the criminal justice system by expanding prisons and getting tougher on criminals.