When Mayor Willie Brown Jr. put troubled youths on city buses as security patrols in 1996, many residents derided the plan, but now the mayor says the program has been an unparalleled success, reducing crime and keeping the peace on bus lines that travel through some of the city's toughest neighborhoods.

Brown said recently that he intended to expand the program dramatically, possibly doubling the budget and staff, to increase the program's visibility and effectiveness."The mayor was lambasted when he put this program out there," said P.J. Johnston, the mayor's spokesman, "but he had faith that given the opportunity, these kids would do a good job, and they have."

The San Francisco Municipal Railway, or Muni, the system that provides bus, train and streetcar service to the city, has been Brown's Achilles' heel since he took office in 1996 and pledged to make improving the system one of his priorities.

City residents say the buses do not run on time, the trains regularly plow through red lights and the system is plagued by technical problems. In November, the National Transportation Safety Board warned city supervisors that those problems could soon lead to a catastrophic accident, unless the city began a comprehensive review of training, management and safety procedures.

Persistent security problems have also troubled Muni riders, with parents and elderly people complaining that the buses are not safe. In January 1997, for example, students from Immaculate Conception, a girls' high school, met with city officials to complain that they had been harassed, beaten up by teenagers and even robbed of chocolate candy they were selling for a fund-raiser.

The program that placed civilian security patrols on buses was begun in early 1995, by a handful of young people, many of whom were former gang members or had had run-ins with the law. They decided that they wanted to help make their neighborhood buses safer. They called themselves Together United Recommitted Forever, or simply the Turf Group.

For about six months, Turf members worked as volunteers on city buses, until a nonprofit group in Los Angeles offered to pay them an hourly wage. Brown took notice of the program shortly after he was elected in 1995, and the city recognized the program in early 1996, renaming it the Municipal Transit Assistance Program, but did not finance it.

When the financing from the nonprofit agency was depleted in June, Muni, the San Francisco school district and the city police department all pitched in to finance the program.

Last month, Muni finally adopted the program as its own, hiring 28 workers at $8.57 an hour for workdays that generally run from 10:30 a.m. to 7 p.m.

"I know they are appreciated by the senior citizens, who stop them and thank them," said Robert Mason, executive assistant to the general manager of Muni. "The school district is happy with them. I've also had a good response from the operators who have called and requested their assistance."