Sometimes those people hit with the highest fuel bills are the least able to afford the time and money needed to lower their bills over the long run.

Convinced that low-income homeowners largely have been bypassed in the rush of "how-to" energy-saving projects, Leanne Sowande-Brent, a mother of four from Evanston, has developed a unique energy-help program for local residents.

The emphasis, a step beyond weatherization, is on installation of passive solar systems wherever an energy audit deems it feasible. The hope is that fuel bills can be whittled by 30 percent to 50 percent.

The program, called Urban Ark, like its biblical counterpart has a distinct rescue mission. It is in the first year of an assured three years of Community Development Block Grant funding through the City of Evanston. So far, its small team of part-time architects, mechanical engineers and minority contractors hae fitted only two homes with solar devices. But another seven homes are to be equipped by early next year, and a total of about 30 are to be completedby 1982. The primary thrust is on heating space rather than water, and the cost per job averages about $3,000.

"Not that much work has been done to develop low-cost solar systems for individual homes, and if someone has to investigate it all on his own, the chances are he's not going to act," said Sowande-Brent, who two years ago took a sharp cut in pay from her job in private industry to work full time for another environmental group in Evanston.

"The things we were doing there were very worthwhile, but it soon became apparent to me that we weren't reaching low-income and minority families," she said. "Many are juggling two or three jobs and can't afford the luxury of attending a Saturday energy workshop. . . . It's not enough to offer good information. We're practitioners -- not just theoreticians."

Convincing low-income homeowners of the advantages of going solar, said Sowande-Brent, was no problem at all.

Everyone has heard of skylights, though they may only think they're for New Mexico or Arizona and not for older building (an Evanston specialty) in an urban setting, she said. "We stress simplicity. We say, 'This is the same knowledge our grandparents had.'"

In one or the two completed projects, a hard-to-heat attic apartment with no windows was equipped with skylights to let in sunshine.

"It's so comfortable now without the heat on," said the owner, who is sure she will save on heating bills this winter.

In addition to supplying technical advice, the Urban Ark also has launched a cooperative buying club to offer such energy savers as window quilts, firewood and wood stoves at far less than the going retail price. Sowande-Brent hopes eventually to develop an energy credity union that could make energy conservation loans to those needing them.

Still another project on the Ark's drawing boards is a plan to buy up an abandoned Evanston elementary school, install solar heating, and convert it into 25 to 30 low-income apartments. A community greenhouse for a year-round vegetable and herb garden and a cannery also are part of the demonstration plan.