A total of $6.1 billion -- nearly one-fifth -- of President Reagan's $34 billion in tentative domestic budget reductions would come from programs for the poor, according to an analysis to be released today by the Center on Budget and Policy Priorities.

In a separate study completed yesterday, the National Association of State Budget Officers, an affiliate of the National Governors' Association, said more than half of the proposed cuts, including many of those in programs for low-income people, would increase financial burdens on state and local governments.

Both analyses are based on Office of Management and Budget statistics showing how various programs would be affected by budget slowdowns and changes tentatively approved by the president and given to the Cabinet and Republican congressional leaders last week. The figures represent reductions in projected spending levels that otherwise would be reached in fiscal years 1986 through 1988.

The study by the Center on Budget and Policy Priorities, a frequent critic of Reagan administration policies on low-income programs, shows that:

* In fiscal 1986, programs aimed primarily at poor and low-income people would be cut $6.1 billion. This constitutes 18.1 percent of the nearly $34 billion in domestic budget cuts Reagan has approved so far.

The programs include Medicaid, which would be cut $1 billion, rural housing, $2.2 billion, Community Services and the Legal Services Corp., which would be terminated, Supplemental Security Income for the aged, blind and disabled, where the routine annual cost-of-living increase would be canceled, Head Start, various housing and health programs for the poor, means-tested veterans' pensions, the special food programs for poor children and pregnant women, welfare for families with dependent children and various other programs.

* In fiscal 1987, cuts in programs for the poor would total $11 billion, 18.4 percent of the $60 billion in domestic cuts approved by the president for that year.

* In fiscal 1988, the cuts would total $14.2 billion, 19 percent of the $74.6 billion in domestic cuts Reagan has approved for that year.

For 1986, 1987 and 1988, these cuts in programs for the poor add up to $31.3 billion.

Center director Robert Greenstein, a former director of the Agriculture Department's Food and Nutrition Service in the Carter administration, said his figures underestimate cuts in programs for the poor because they do not include the impact of proposed reductions in programs that are not aimed at the poor but have a large effect on them, such as Medicare, urban mass transit, services for the elderly and Urban Development Action Grants.

Greenstein said that under the administration proposals, about 2 million low-income recipients of both Social Security and SSI in effect would lose their Social Security cost-of-living adjustments because their SSI benefits would be cut automatically as soon as they start receiving the Social Security COLA.

Other program losses: 500,000 low-income pregnant women, infants and children would lose prescription food supplements because of a 17 percent reduction in the caseload for the food supplement program (called WIC) necessitated by cuts in that program. In addition, Greenstein said, 20 million food stamp recipients' benefits would be frozen despite rising food costs, so benefits for a family would fall below the amount needed to purchase the government's lowest-cost food plan.

He said subsidized housing would be provided to 200,000 fewer families eventually because new construction would be stopped.

Greenstein calculated that if the low-income program cuts are added to cuts in other non-low-income programs that the government classifies as "human resource programs," reductions from 1986 to 1988 would total $63 billion -- as much as all the Reagan human resource cuts (other than Social Security) enacted in 1981-82.

The Budget Officers' study said $17 billion of the president's $34 billion in cuts for fiscal 1986, $37 billion of his cuts for 1987 and $43 billion of his cuts for 1988 would have an impact on states and localities.