Only the narrow entrance to San Francisco Bay, the Golden Gate, separates the City of San Francisco from Marin County.
That's geographically. But the space between the two can seem vast when viewed from other perspectives - say, housing.
San Francisco Mayor Dianne Feinstein recently announced a drive to provide shelter to the indigent, whose numbers recently have increased substantially. Her hope, she said, is to get everybody off the streets and into ''safe, sanitary shelter'' by Christmas.
Just across the Golden Gate Bridge, the Marin County Housing Authority has announced a more grandiose program for putting a roof over one's head. The county will subsidize low-interest mortgages for people earning up to $58,000 a year to buy homes. Those prospective homebuyers aren't having to sleep in their BMWs these days. But in Marin, the fifth-wealthiest county in the United States, home is $140,000 to $150,000.
A Marin housing official says prospective buyers making $50,000 to $60,000 a year have difficulty qualifying for loans. So the county will issue $50 million in tax-free bonds, which pay 10 percent interest, and use the money to provide, through local lending agencies, 30-year mortgages below prevailing interest rates. The loan program, authorized under state law, will begin sometime in 1983 .
Back across the bridge, Mayor Feinstein announced at the end of last week that 331 additional beds had been made available to the homeless in San Francisco. She said that before the recent drive began there were 998 free beds available. Not all of the added beds were being used, said the mayor, probably because many of the indigent who are new to the city had not learned of their availability. She added that if the beds are not filled in coming days, the city will assume that the need has been met.
Mayor Feinstein and other officials say they know the number of indigent people in the city, including many families, has grown in recent months because of high unemployment in the state and the nation. California, with its mild climate and reputedly vigorous economy, is one of the states to which job-seekers have been drawn. Also, San Francisco's generous assistance to people ineligible for welfare - $248 a month - is believed to have drawn many jobless from other states.
The plight of the homeless in San Francisco has been brought into sharp focus by unusually cold and stormy weather in recent weeks. Public and private facilities that provide food and shelter for the indigent have not been able to keep up with the growing need.
As a stopgap measure, the city parked two inoperative buses in the ''Tenderloin,'' a district noted for street sleepers, when the weather turned bad. But when it was discovered that some of the 75 people sleeping in the buses were preying on others and that the vehicles were being vandalized, the mayor ordered them removed, then followed up with the new shelter program.
There is some criticism of Marin's housing subsidy for the affluent, but no action to block it is expected. Since most of the houses to be financed are expected to be new, it is seen as a stimulus for the housing industry.