Boston officials are offering to pay new landlords to keep their apartments affordable.

The Walsh administration Tuesday will announce a $7.5 million program to help community groups and small landlords buy apartment buildings, if they agree to keep existing tenants in place and maintain rents at levels that low- and moderate-income tenants can afford.

The program will try to counter the wave of changes in neighborhoods around the city, where investors are buying buildings, pushing out tenants, and dramatically increasing rents. Tenant groups have been lobbying the city for additional protections for renters and other efforts to keep Boston’s existing housing stock affordable.

And city officials say they agree.

“The administration is extremely concerned about displacement,’’ said Sheila Dillon, chief of housing for Mayor Martin J. Walsh. “Tenants have lived in these buildings for years, for decades, and they’re being pushed out. We need to come up with strategies to address this.’’

The new program would provide a loan of up to $75,000 per unit to help affordable housing developers and small private landlords compete with market-rate investors to buy occupied apartment buildings. In exchange for the city financing, the new owners would have to agree to keep 40 percent of the units affordable to low- and middle-income renters for 50 years, and that no tenant in good standing will be evicted.

The money, she said, could help make it possible for community groups to buy more buildings and keep them affordable. Housing advocates agreed, though they noted that in some fast-changing neighborhoods, even $75,000 a unit doesn’t go all that far.

“The general reaction I hear from affordable developers we’ve talked with is, ‘That’s really interesting, but I don’t know if it works at $75,000,’’’ said Steve Meacham, organizing coordinator with tenant-rights group City Life/Vida Urbana. “Given that rents have to be affordable for 50 years, you have less to play with in terms of how much you can offer.’’

Still, Meacham said the program could make a real difference in neighborhoods such as East Boston, where his group and others are organizing renters facing eviction, and pushing owners to sell their buildings to local nonprofits instead of clearing out tenants.

“Anything that makes it easier to acquire these buildings helps,’’ Meacham said.

Right now, the project is a one-time effort, with $7.5 million enough to fund about 100 units. The money is coming from a city affordable housing pool that developers pay into when they build new market-rate apartments and condominiums. If successful, it would be renewed in future years.

Meanwhile, Dillon said the Walsh administration is still reviewing a so-called “just cause eviction’’ law, which requires landlords to meet certain conditions if they want to evict tenants, such as nonpayment of rent. The measure is now before the City Council. Landlords say it would make it hard to evict renters under any circumstances, driving up rents in other properties and slowing real estate investment.

Meacham said the city should be broadly discouraging building owners who use mass eviction as part of their business model.

“We support anything which says ‘We’re not going to make that easy for you,’’’ he said. “We consider all of it to be part of a well-integrated strategy.’’

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.