Almost lost in the outcry against Reagan administration tax reform proposals is the plight of the poor who need low-income housing, which would be dealt a crippling blow, critics of the plan say.

The tax plan would wipe out the tax benefits that attract investors and developers to build and rehabilitate housing for the poor, leaving few other ways to pay for low-income housing, said Barry Zigas, president of the National Low Income Housing Coalition.

Massive cuts since 1981 have reduced federal spending on low-income housing by 60 percent. The administration's fiscal 1986 budget proposes additional cutbacks, but so far most have been rejected by Senate and House committees.

The number of households needing low-cost rental housing is more than double what is available in the private market, according to an analysis of 1980 Census figures made by the coalition. Nearly 4 million households -- about 10 million people -- now live in public housing or receive government rental assistance. The average waiting time for public housing and rental assistance payments in major U.S. cities is nearly two years, with some cities reporting much longer waiting times, surveys show.

The waiting times in the Washington area range from two to three years in Arlington to seven years in Alexandria, according to local agencies and the Department of Housing and Urban Development.

The people who live in government-assisted housing are "the poorest people in the United States," the majority of them elderly or single women with children, Zigas said. Their median income is $6,275 a year, when the median for all Americans is $20,885. The estimated 8.4 million individuals and families who rent their homes in either private or public housing earn less than $7,000 a year, according to federal surveys.

The limited federal contributions have left state and local governments and private groups with much of the responsibility for sheltering the poor. But without the lure of generous tax breaks, little low-income housing could be built, according to representatives of community and nonprofit organizations in five cities, who spoke at a congressional briefing this week.

Private investors seeking tax benefits make up about 25 percent of the financing packages put together for low-income housing construction and rehabilitation projects now, according to Robert Zdenek, president of the National Congress for Community Economic Development.

"It's clear that the involvement of the private sector depends on their capacity to make money," said Cushing N. Dolbeare, chairman of the housing coalition. Investors "can't make it on cash flow in low-income housing, so they make it on the tax shelters."

State and local governments and community groups "have tried a lot of new things in the last couple of years" to finance low-income housing, but many of their efforts were designed to "integrate" with federal tax provisions, she said. Without the tax benefits, "there really isn't a way . . . for states and local governments to put up the resources that are necessary to subsidize housing."

Money from private sources made the difference when the Tri-County Community Development Corp. in Charles County sought to build rental housing for poor rural families, Dana Jones, of the nonprofit, private development corporation, said at the congressional briefing. The families had been displaced when subdivisions sprang up to accommodate middle- and high-income residents brought by the "Beltway boom and the growth of military installations" in southern Maryland, he said. The tax breaks available brought investors into the organization's construction project, and the resulting housing now shelters families with annual incomes as low as $6,000, Jones said.

Reagan tax plan changes with the most impact on low-income housing would:

Substantially reduce the dollar value of most tax deductions, with the result that investment in housing and community development projects would become much less attractive for people in the 50 percent tax bracket. The deductions affected would include depreciation, tax-exempt financing, deferred and current interest, charitable contributions and capital gains exclusions.

Reduce the current range of tax rates on corporate income -- from 15 to 46 percent -- to 33 percent on taxable income of $75,000 or more, with lower rates for income under $75,000. The effect would be to lower the value of tax deductions for corporate contributions and investment in real estate syndications.

Eliminate the five-year writeoff of expenses incurred in rehabilitating housing units occupied by low-income residents, under 167(k) of the tax code. "The negative impact on low-income rental housing rehabilitation would be significant" because the deductions in the first years of a project are most important in syndications, according to an analysis of the administration tax plan by James Pickman and Associates Inc., a Washington firm.

Do away with the preferential depreciation allowances for low-income housing, which are more favorable than for any other real estate investments.

Eliminate the 25 percent tax credit available when housing for low-income families is part of historic preservation projects.

Revoke the tax exemptions of industrial development bonds for multifamily housing and single-family mortgage revenue bonds. State and local governments often use these bonds to give developers below-market interest rates. In return, 20 percent of the housing units built must be reserved for low-income households for 10 years or the life of the bond, whichever is greater.

Increase the depreciation period for low-income property from 15 years to 28 years, and no longer permit accelerated depreciation.

Extend "at-risk" rules to real estate partnerships. Generally, a taxpayer may deduct tax losses from an investment only in the amount of money he has at risk, that is, funds actually invested and borrowed money for which he is personally responsible. Investors in real estate limited partnerships, however, also can deduct losses equal to their allocated share of debt for which no partner is personally responsible, an important consideration for investors in low-income housing.

Subsidizing low-income housing through tax preferences is an inefficient and costly way to provide for the shelter needs of the poor, housing advocates acknowledge. It is important, however, "to recognize that with the demise of Section 8, which I did not think was a good program, that we need some alternatives to fill the gap," said Cicero Wilson, of the American Enterprise Institute Neighborhood Development Project. "If your options have been cut off because $8 billion in Section 8 funding is already gone," changing the tax provisions may be "the final nail in the coffin."

The Section 8 new construction program was the government's major means of financing low-income housing until it was allowed to expire in 1983. It provided hundreds of thousands of units, but at high cost with generous subsidies and benefits for developers and landlords, producing a number of scandals.

Reagan administration backers of eliminating investor tax benefits say it is a way of saving billions for the federal treasury, but critics say it would be a drop in the bucket compared with the amount lost to the government through housing subsidies for affluent Americans.

Congressional figures show that only about 13 percent of the total tax expenditures for housing -- the amount lost to the federal government through tax benefits -- over the next five years would be saved by eliminating preferences for real estate investors, according to Zigas. In 1986 alone, investor deductions will amount to about $7 billion while homeowner deductions for mortgage interest, property taxes and other tax breaks will amount to $46 billion, he said.

Responding to criticism that opponents of eliminating investor tax breaks have not come up with alternative ways to save money, Housing Coalition Chairman Dolbeare proposed to "convert the mortgage interest deduction into a 20 percent tax credit," probably saving from "$10 to $15 billion a year." The savings should be targeted to pay for low-income housing needs, she said. A deduction is subtracted from income before tax is figured, and a credit is taken from the tax bill.