IT TAKES NEITHER financial wizards nor welfare softies to understand what a Maryland state advisory commission has just pointed out about pulic assistance payments in the two nearby counties -- that high rents are eating up most of the money. The current minimum standard used to calculate eligibility for public assistance in Maryland is $259 a month, which officials say is one of the lowest in the country. Yet the state commission estimates that a family of three needs at least$507 a month "to maintain a minimum decent standard of living." In Montgomery County, this average family of three is getting a check for $250 -- and paying about $240 in rent. The math for Prince George's County is equally grim.

"Ridiculously low," says Edward R. Bloom, deputy director of Montgomery's department of social services. He believes the 2,873 county families participating in the Aid to Families with Dependent Children program are getting only half the amount they should. Williams Davidson, director of the Prince George's department, calls the figures "disgraceful." State officials agree. Gov. Harry Hughes raised AFDC payments by 10 percent with a $4.8 million increase, in a 1980 budget of $4.8 billion; and he has now requested new projections for the next budget. So if all these officials agree that higher payments should be made -- Maryland now ranks about 34th among the states -- what's the problem?

Coming up with the money is one part of it; figuring out how best to distribute it is another. The federal government reimburses the state for 50 percent of the state's payments. But Maryland officials estimate that it would cost $250 million in general fund revenues to cary out the commission recommendations -- an amount that simply won't be available. It comes down to a trade-off: if the standard is raised, more people become eligible, and the more people in the AFDC program, the more who are eligible for Medicaid. If the actual grants are raised instead, there would be more money for those already in the program.

These are not appealing alternatives, and the counties, strapped by TRIM and other financial constraints, cannot be expected to come up with hefty supplements.Some higher standard should be adopted, but the emphasis should be on raising the actual monthly payments to those who are the poorest. It will be up to Gov. Hughes to make this case in a strong and realistic way to the legislature in the next session.