The Senate Finance Committee's tax revision bill, which the full Senate is expected to debate next week, would make major changes in tax benefits that attract most of the financing for low-income housing construction and rehabilitation, drawing charges that the proposed legislation's impact could be devastating.

The bill eliminates tax shelters now used to entice investment in low-income housing and it substitutes a new system of tax credits. Restrictions were placed on use of the tax credits late in the committee's deliberations, however, making them ineffective as a means of attracting capital, according to representatives of several national organizations representing low-income and rental housing interests.

Sen. George J. Mitchell (D-Maine) said he plans to introduce an amendment that would make the tax credits more workable.

"I generally favor the principle behind the bill . . . that we should be reducing tax incentives and permitting investments to be made on economic grounds . . . ," Mitchell said. "But it's clear that low-income housing is not economically feasible. Without some level of government participation it simply won't be built."

Virtually all the federal programs that directly subsidized construction and renovation of low-income apartment projects in the past have been killed by the Reagan administration. As a result, nearly all of the low-income housing built in recent years has been paid for by investors seeking the generous tax benefits available and by state housing agencies using tax-exempt bond financing and community development grants.

Anthony Downs, a housing expert and senior fellow at the Brookings Institution, said that although the Senate bill would "reduce the attractiveness" of investment in multifamily housing, much of its impact could be offset by the housing construction being encouraged by low interest rates.

"Historically, the way low- and moderate-income people get housing is through the trickling down of housing vacated by higher-income people which then becomes available to the low-income," he said. Although inadequate if it is the only means of providing housing, trickle-down "works best when the total number of additional units built exceeds the total number of households formed." He said household formations in recent years indicate that about 1.5 million will be set up in 1986, while builders are expected to produce about 2 million new housing units in 1986, including about 300,000 mobile homes.

Most low-income housing advocates believe, however, that the loss of tax incentives will be a more serious problem. Little new housing for the poor will be built, and units leaving the subsidized housing stock through foreclosures or conversion to higher-cost dwellings will not be replaced, they predicted.

Tax credits are "the good news" in the Finance Committee bill because they are more directly linked to individual units occupied by low-income households than past tax subsidies and place rent restrictions on tax-subsidized units, according to Barry Zigas, president of the National Low Income Housing Coalition.

The bad news, Zigas and representatives of other housing organizations said, is that the credits are not available for structures receiving other federal subsidies, including tax-exempt bonds, Community Development Block Grant or Urban Development Action Grant funds, Farmers Home Administration loans for rural housing or Section 8 rental assistance. Investors in existing projects having government loans or federally insured, low-interest-rate mortgages also would be ineligible for the tax credits.

This restriction renders the credits virtually useless, "because the credit alone won't replace both the tax deductions eliminated by the bill and other federal assistance," Zigas said.

Mitchell's amendment would permit investors to take the tax credits for projects that receive other government assistance. The amendment also would make people who invest in existing low-income housing projects eligible for a 4 percent tax credit if half the units are rented to families with incomes less than 50 percent of the median for their community. Without tax incentives, new owners of low-income housing developments that have reached the end of their regulatory commitments probably would convert the buildings into condominiums or higher-rent projects, a Mitchell aide said.

If the finance committee bill becomes law, investors in newly constructed and substantially rehabilitated multifamily buildings would get an 8 percent tax credit per year over 10 years for all units occupied by "very low-income" families -- those making less than 50 percent of the median income for their area.

Investors also would be eligible for a 4 percent credit annually for up to 30 percent of a project's apartments occupied by families with incomes between 50 and 70 percent of the area median.

Another provision of the bill would make major changes in current law, under which investors can use a real estate project's losses as tax deductions against income from nonreal estate sources, such as salaries and other types of investments. The often hefty losses of low-income housing developments are virtually the only attraction for private investors, because the projects rarely offer the major advantages of other investments -- income from rents and increases in property values.

The Senate tax bill would sharply curtail deductions of these so-called passive losses for low-income housing investors whose annual incomes are less than $100,000. The deductions would be phased out as investor incomes rise and eliminated entirely for those with incomes of more than $150,000.

Housing advocates say the investor deduction allowed in the proposed tax revision -- for $25,000 in passive losses or $6,750 in the new tax credits -- is so low as to be unattractive to high-income investors, the ones most likely to be looking for tax benefits.