The president's plan for welfare aid to Cuban and Haitian refugees probably will end up helping for fewer people and on a stingier scale than the original announcement last week suggested.

One major reason is that the plan is based on state welfare laws and the state most involved -- Florida -- has a relatively limited welfare program.

Florida, where 55,000 of the 129,000 potentially eligible Cubans and Haitians now live, provides relatively low benefits and has tough eligibility requirements.

According to some estimates, fewer than half the 55,000 -- perhaps only 10,000 to 15,000 -- may actually qualify for aid in Florida. The rest would be out of luck.

Under the president's plan, the newcomers would have a special legal status and would be eligible for federal-state welfare aid under existing state rules, which differ from state to state.

Welfare theorists have often complained that the states have too much latitude to pay low benefits and impose tough eligibility rules. The Cuban boat people illustrate what they mean.

Under the president's proposal, refugees can get aid if they are eligible for one of the existing major federal-state welfare programs, such as SSI (Supplemental Security Income), Aid to Families with Dependent Children (AFDC) or Medicaid.

These programs, however, have sharp limitations on eligibility, which in Florida are somewhat more stringent than in many other states. Generally, in all states a low-income person can qualify for the programs only if he or she is either aged, blind or disabled or a member of a family with minor dependent children.

This means that large numbers of people who don't meet these qualifications -- such as married couples without children, nonelderly single people, or, in the case of Florida, families where an unemployed father is present -- won't qualify. (Other places, such as the District of Columbia, New York and two dozen other states accept families with an unemployed father, but not Florida.)

Moreover, each state sets a ceiling in income a recipient can receive from nongovernment sources and still qualify, and Florida's is relatively low $230 a month for a family of four. Other states have much higher qualifying levels.

What all this adds up to, according to U.S. government officials here and Florida welfare officials in Miami and Tallahassee, is that a large portion of the 55,000 potentially eligible people in Florida may be denied assistance. o

The president did provide a safety net by asking that Congress reimburse the states for outlays for support and medical care for persons ineligible for aid under SSI, AFDC and Medicaid. A cash payment to a person who is destitute, but ineligible for these other programs is made in some states under state-funded programs named "general assistance."

Florida, however, hasn't any general assistance program, emergency or medical assistance outside Medicaid.

Dade County, which surrounds Miami, does have a general assistance program of its own, but officials said in a phone interview yesterday that a person must be medically unable to work to be eligible, and unless this rule is changed, most Cuban and Haitian refugees won't qualify. So, again, half or more of the 55,000 may qualify for nothing. (Congress, of course, could change all this by rewriting the president's proposal.)

For those who do qualify, florida's AFDC payment of $230 a month for a family of four without other income is low when compared to D.C., where the same family would get $348 (about the national average as of September) or New York, $476.

President Carter also wants the states to assume a far larger share of the financial burden for the Cubans and Haitians than any area had to assume for the 300,000 Indochina refugees.

Under the federal welfare law, the government reimburses each state for anywhere from 50 percent to 78 percent of its outlays for AFDC and Medicaid, but zero for general assistance, since people on general assistance don't meet the qualifications for federally funded programs.

But under the Indochina program, the government reimburses the states for 100 percent of their AFDC, Medicaid and general assistance outlays.

Not so under the administration's Cuban/Haitian plan. Carter is proposing that state AFDC and Medicaid expenses be reimbursed under the existing basic welfare law ratios, which means Florida would get back only 59 cents of each dollar it spends.

For those states which help some Cuban and Haitian refugees, otherwise ineligible, by using the general assistance backup net. Carter is proposing a 75 percent reimbursement rate.

David Voss, spokesman for the Florida Department of Health and Rehabilitation Services, said Florida officials believe these lower reimbursement ratios for the Cubans and Haitians as compared to Indochinese are unfair: "It puts an undue burden on the Florida taxpayer for what is basically a national problem and a national policy decision."