In a perverse but important way, New York City performed a service for the nation through its fiscal crisis. From coast to coast, mayors and councils and citizens' groups began to examine their own cities' financial practices, to make sure they weren't falling into the same trough of red ink.

Now New York, on a more positive note, is showing the country what a city's people, through volunteer and self-help efforts, can do to compensate for sliced budgets and to make their own neighborhoods upbeat, pleasant places to live.

The story is told in a new, 140-page "New York City (630 Fifth Avenue, New York, N.Y. 10020), it is probably the most exhaustive listing ever compiled of what citizens, on their own, can do to enhance the quality of life of their city. All of the hundreds of citizen efforts listed in the handbook are now taking place, sometimes in hundreds of locations in New York's boroughs.

The self-help binge doesn't mean that all of New York's familiar selfishness, cynicism and impersonality has been expunged. Crime (albeit reduced), indifference and exploitation remain. But only the most hard-bitten skeptic can dismiss the sense of small-town community spirit and cooperation that's sprouting on the city's blocks.

The Self-Help Handbook starts with a section on community crime prevention, including block-watcher programs, civilian car and foot patrols, auxilliary police officers and alarm systems. It goes on to parent safety patrols, property identification systems and a buddy alarm system for merchants.

Fire prevention comes next, with suggestions on how to set up volunteer fire-warden groups and fight false alarms. To back up the badly undermanned sanitation department, there are programs for block cleanups, sidewalk sweeps, litter baskets, graffiti removal, recycling centers, neighborhood dog runs and anti-litter campaigns. There are programs in community gardening, playplots, mural painting, bench painting, and how citizens can adopt and care for street trees.

The handbook reviews many programs for children, ranging from street olympics and volunteer tutorial programs to trips for youth, family day care and turning residential blocks into daytime play streets. For senior citizens, there are suggestions for local-merchant-discount programs, medical and food-supply delivery to home-bound people, escort services and telephone reassurance.

Citizen self-help was clearly needed when New York plunged into its fiscal crisis in 1975. But the Citizens Committee, founded that year with foundation support, has been in invaluable catalyst. It ran public service ads asking "greedy, heartless New Yorkers' to volunteer for work in city or social service agencies. It got 8,000 responses, and placed 2,000 volunteers. To spread the self-help gospel, the committee maintains a speaker's bureau, utilizes the media and has assembled a mailing list of 8,000 block associations, civic groups and concerned citizens.

The outside world is generally unaware of the "vibrant" life of New York's neighborhoods, says Osborn Eliott, chairman of the Citizens Committee. Of the city's 35,000 blocks, some 10,000 have organized block associations. The Citizens Committee believes it may have inspired 2,000 to start up. Active in areas from crime control to credit unions, the block associations have begun to replace New York's declining political clubs as mini-governments at the grassroots level.

At annual Citizens Committee dinners, awards are given to unsung New York heroes - people like Patricia Cordes, who set up teams of students to stop false fire alarms in an arson-torn section of the South Bronx; and Jackie and Dennis Canning, who organized their Brooklyn block to drive out prostitutes and drug pushers (one method: bombarding pimps with balloons filled with water from rooftops). The Cannings also converted a vacantM rat-infested lot into a children's playground and garden.

When the blackout and looting hit New York last summer, the Citizens Committee administered a $3 million emergency fund to encourage owners of vandalized businesses to reopen their doors - and some three-quarters did. The organization launched a "Citizen Sweep Corps" and gave away 5,000 brooms to volunteers willing to sweep their sidewalks regularly. And it has made hundreds of small grants to groups that need a little seed money ($1,000 limit, usually less than $100) for projects. A $70 grants stimulated several Manhattan women to collect $2,000 in contributions from department stores and use the proceeds to plant 3,000 flowers in front of the New York Public Library.

Elliott hopes New York's self-help record will soften congressional hearts when further emergency assistance is debated this spring. Political reality dictates Congress probably won't act unless it thinks bankruptcy is imminent. But by any objective scorecard, the city has made immense strides since 1975.

It may be years before New York is completely "out of the woods." But the despair of 1975 has given way to cautious optimism in 1978. And for that, a lot of credit goes to New Yorkers who have cared enough to help sustain their neighborhoods - and thereby their city.