In the early evenings, Sister Agnes Hagen travels inner-city streets in her faithful 1964 Dodge, armed with her flashlight and trusty real estate listings, searching for low-priced houses her clients to buy.

As a real estate agent, Sister Agnes is a fast talker who preaches the ins and outs of property values to her home hunters.

In Baltimore, where the founders and followers of the renaissance believe the key to a healthy city neighborhood is homeownership for both the poor and rich, it is not as surprising to find a nun selling real estate as it might be elsewhere.

Sister Agnes works for the nonprofit St. Ambrose Housing Aid Center, where she has sold 125 houses in the last 4 1/2 years.

She specializes in low-income home buyers who never have owned property and often are overwhelmed by the responsibilities, even though they realize their mortgage payments may be lower than monthly rents.

While she drives her home hunters through the city, Sister Agnes talks real estate as if it were second nature.

One recent evening, she took Yvonne Spellman around on Spellman's first evening of house hunting.

"You've got to decide on your priorities," Sister Agnes told her. "You've got to look at the neighborhood, see if it's near a congested street. Go there around dinner time and see if people and hanging around the street corner or if it's quiet."

Spellman, a nursing technician at Mercy Hospital, has lived 16 years at Latrobe Homes, a public housing development.

As in all government-subsidized housing, her rent increases as her salary goes up. Her friends tell her it's time she invested in a house.

But she confessed her apprehensiveness to Sister Agnes.

"This is the first time I've done this," she said. "I've never been able to make the move before."

Inside each house, Sister Agnes showed Spellman how to look for defects that need repairs.

The real estate agent pointed her flashlight at stains on the ceilings where water has leaked, pressed her feet on sagging linoleum floors and shook her head at galvanized pipes and decrepit furnaces.

Spellman, a single woman who is head of her family, is typical of Sister Agnes' clientele.

A year ago, with Sister Agnes' help, Cynthia Darden bought her first house.

Darden paid $7,000, making monthly mortgage payments of $97, or $100 a month less than she paid as a renter in a previous house.

"I had never bought a house before," she said. "I didn't have a car, so Agnes drove me everywhere and helped me with everything."

Darden, a maintenance worker at the Baltimore-Washington International Airport, lives in her two-story rowhouse with her 7-year-old daughter.

She said she loves owning her own home, despite the fact that the porch collapsed last week. "I've got to find some way to fix it now."

Darden was surprised when told her real estate agent is a nun.

"You're kidding," she said. "She never told me."

Sister Agnes' colleagues refer to her simply as "Agnes." And she does not introduce herself by the term "sister."

"It's an unnecessary formality, like Mr. or Mrs.," she said.

Despite her success so far, Sister Agnes worries about the increasing difficulty of finding affordable houses for people such as Spellman and Darden.

In her office in the back room at St. Ambrose, Sister Agnes sits beside a bulletin board covered with snapshots of rowhouses her clients have bought over the years.

The board looks like Sister Agnes' inner-city version of one of those real estate layouts of suburban homes that often appears in the Sunday papers.

She pointed to the houses on the board -- her own "gallery of homes."

"Practically every house sold for $20,000," she said. "Most of those houses would now go for $35,000. The average Baltimore family cannot afford the average Baltimore house -- even if they are debt-free. There's something wrong with that.

"I think inflation has caught up with the Baltimore market."

She said she hopes the city's pending mortgage program will help her clients. But the program, which depends on the sale of revenue bonds to provide low-interest mortgage loans, has been stymied by the inflationary economy.

Sister Agnes, 42, has been a nun since 1956 when she joined the order of the Sisters of the Holy Names of Jesus and Mary in Montreal.

For 18 years, she taught remedial reading in Washington. When she switched to selling real estate, she moved to Baltimore to work for St. Ambrose.

"I didn't look at it as selling real estate. We see it more as a social service, more like social work. One sister in my order works in a factory in Tennessee where she is a stitcher. She is an organizer for better working conditions."

Sister Agnes' boss, Vincent Quayle, director of the St. Ambrose Housing Aid Center, can hardly believe his good fortune in having her as the sales agent for St. Ambrose non-profit Charm City Realty.

"She's the ideal person to do the job," said Quayle, the real estate broker for Charm City. "With her energy, she seems not to mind working nights and on weekends. If we didn't have her, many families would not have bought houses.

"She seems to thrive on competition. Maybe the religious thing has motivated her through a nonmonetary satisfaction. If Agnes were selling houses in the suburbs, she would be a wealthy woman today."

Quayle, a former priest himself, estimated Sister Agnes grosses $20,000 in commissions each year, half of which goes to St. Ambrose and half toward her salary.

He said some of her counterparts in the real estate industry may envy her energy and success.

"The reason why I love her being a nun is the industry can't publicly criticize a Catholic sister who's selling houses to poor folks," he said. "I think they're jealous. They know she's a good agent and they would love to have her working for them."