New approach to aiding runaways is keeping many off the street. Center provides more than bus ticket home

With jeans, a bulky sweater, and no makeup, she looks more like the adolescent tomboy next door than a streetwise runaway. At 17, Susan (whose name has been changed for this story) has no home. She's been the ward of an East Coast court for 12 years, bouncing from orphanage to boarding school, and reform school to foster homes. She has lived on the streets of Boston, Philadelphia, and Miami. This is her third ''escape'' to San Francisco, where she has, on occasion, resorted to prostitution to get money for food or a place to sleep.

But this time she found her way to the Larkin Street Youth Center, and she says it's the first place that has offered her respite from street life without the threat of sending her home. Except for a few scattered services like overnight shelters or halfway houses, the United States has no social-service network specifically for homeless teen-agers. And Larkin Street's success as a multiservice program - backed by political support in the community - has been called the ''wave of the future'' for homeless youth.

''If a baby shows up on a doorstep, it's given protection, . . . a system exists to help. But if you find a teen-ager, rarely does he get help,'' says June Bucy, executive director of the National Network for Runaways and Youth Services, in Washington, D.C. ''Kids are floating around without any access to the system,'' she says.

The aim of the Larkin Street private center, organized by a consortium of local small businesses, churches, community groups as well as social workers, is to provide the services it takes to keep homeless youth from hard-core street life, where prostitution is a common way to make money.

Of the 137 youths who have used the center intensively, 47 percent successfully returned home, 18 percent were placed in stable living situations, 16 percent found jobs, and 19 percent dropped out.

Susan, for example, probably won't go home. But recently, in the 11th day of a self-imposed withdrawal from heroin, she says the center is helping her get into a drug rehabilitation halfway house, where she thinks she can finish high school. In the meantime, she says, Larkin Street has helped her stay ''away from temptations'' on the street by offering food vouchers, referral to temporary shelters, daily counseling, and a comfortable drop-in center.

''If you're not supposed to be here (away from home) in the first place, who's going to help you?'' Susan asks, summing up the dilemma youth and communities face all over the country.

The US Department of Health and Human Services reports that there are more than 1 million homeless youth on the streets - New York City alone is estimated to have 20,000. The problem poses questions for communities nationwide: Is it a criminal-justice issue or a social-service problem? What are the risks of liability in taking in these young people without parental consent? Should a community shoulder the cost of a homeless youth if his parents paid taxes somewhere else?

The solution is often to ''deport them, give them a one-way bus ticket home, '' explains Greg Day, community-relations director of the Larkin Street Center. San Francisco police sweeps to clean up the streets simply result in moving the problem from one neighborhood to another, he adds.

Consequently, when a community chooses to help the children instead of shuffle them about, it's unusual, Mr. Day says. And more, a multiservice program like Larkin is unusual because it addresses the whole condition of a child rather than simply immediate needs.

''Before Larkin Street, the only time we could impact these kids with services was in an emergency, in attempted suicides, drug overdoses, depression. Now with Larkin Street's high visibility, it gives kids more options,'' says Jon Hersztam, program coordinator with the the city's Department of Public Health.

Although the center is considered a success, its one-time $180,000 federal grant (to find solutions to juvenile prostitution) expires at the end of the year. The city's initial $70,000 appropriation is expected to be renewed. But the search for more money is tough, because the subject is an unsavory one.

''This is a problem that in the eyes of many is best forgotten, and, if not forgotten, then it's unbelievable, because people are incredulous that teen-agers could be doing this (engaging in prostitution),'' explains Randy Mecham, executive director of Youth Advocates Inc., which administers Larkin Street.

He says the local response to the problem has been a mixture of practical business concern and civic responsibility - possibly the only way of creating new social services in an era of government cutbacks.

The center is the result of political pressure brought by local merchants, churches, and civic groups. Large numbers of homeless youth spilled over from the seedy Tenderloin district just blocks away into more upscale neighborhoods, where the problems that youth bring are considered bad for business.

The Polk Street Town Hall, one of five groups that provide salaries for employees at the Larkin Street Center, was formed because of the juvenile homosexual prostitution that was a particular problem in the Polk Street shopping district. The impetus for the formation of the group came from businessmen who found teen-agers sleeping on their doorsteps, but felt the solution was not to turn them over to police.

Pressure from groups like the Town Hall prompted creation of the Mayor's Youth Services Task Force, which identified the problem in a report last spring. Among other things, the group found:

* A thousand homeless youth are on San Francisco streets every night, but there are less than 50 beds available at shelters for them.

* Many of the youth are ''throwaways,'' forced away from home often by physical or sexual abuse.

* There is a high incidence of prostitution in this population, or, at the very least, a trading of sexual favors in exchange for necessities.

* Homeless youth are wary of the social-service delivery system - they don't know how to use it, or they're afraid of being turned in.

Larkin Street opened its doors last spring with funding gained as a result of the mayor's report.

Larkin Street's services are not limited to the modest storefront it occupies. Workers try to build rapport with youth in the nearby Tenderloin and on Polk Street, explains Russ Zellers, executive director. Outreach is a part of the center's concept of ''prevention.'' Counselors want to attract youth to the center before they become involved in street life and the nearly inevitable prostitution, he says.

''We look for motivation, because we get demanding of what a young person needs to do - he has to want to make changes in his life,'' Mr. Zellers explains. Youth are limited to six weeks in the program, and the primary goal is to get them to return home - or, if they don't, then to help them ''develop independent living skills,'' he says.

Keeping kids off the street isn't easy, explains Evelyn Poates, clinical service coordinator.

''It's hard to tell a kid to work at McDonald's for $3.35 an hour and ask them to give up their friends on the street, when an hour later they come back and throw $700 on my desk (from prostitution),'' she explains. ''But we try to give them the support system. It seems that if they work a long, hard hour for $ 5, they appreciate it more'' and develop a better sense of responsibility,'' she says.