A BITTER WIND and a frozen crust of snow over the garden bring the usual crisis of household welfare policy: to feed the birds, who are destitute and in need, how much sunflower seed should be wasted on the squirrels, who are neither? It's a familiar question in welfare economics. Arthur Okun used to call it the leaky bucket. How much leakage in the system do you tolerate, in order to meet society's commitments? These are tough times for the sparrows.

As you read these lines, there is a welfare experiment in progress -- not, alas, federally funded -- not far from here. It's the same old experiment. The birds sit on the fence, three squirrels sit on the bird feeder gaily gorging themselves, and the project administrators gloomily watch through the kitchen window wondering what to do about the situation. In recognition of the public statements of the president-elect on this subject, the three squirrels are code-named Waste, Fraud and Abuse.

They are all dexterous and daring, but Abuse is a rodent Houdini, bred through generations of thieves and acrobats to a Darwinian apex of seed-stealing skill. In a narrow urban back yard there is no point where -- via branches, the arbor or the power lines -- a bird feeder is not open to Abuse. He has been seen to leap two yards horizontally through open space. The repeated discoveries of Abuse in the bird-feeding program have brought the same political reaction as Mr Reagan's case of the woman who was alleged to receive 26 welfare checks every month. The need for welfare reform is clear.

Worse, the squirrels have what social workers call hidden resources. There was a constant cascade of acorns throughout the autumn. That's not all. Waste, Fraud and Abuse are more than suspected in the recent disappearance of a dozen expensive tulip bulbs. It is outrageous that these squirrels should not be content with their own generous share of this world's goods. There was a time when life was simpler and a strong sense of morality prevailed. ebut there has been a deplorable deterioration of conduct in the garden, as everywhere else. Now the squirrels eat their own acorns for breakfast and want the birds' seed for lunch. All sense of propiety and honor has vanished. It is probably the result of watching too much television.

As for the latest welfare experiment, and the next round of reform, you won't need to hear how it will all turn out. You already know. After one more cold night the household, against its principles and its better judgment, will fill up the battered feeder again. By mid-morning Waste, Fraud and Abuse will again be in evidence. They will be sitting on the feeder having brunch and carelessly kicking seed off onto the snow below where the sparrows and juncos will pick it up. Talk about a trickle-down welfare policy.

How will it end? You know that, too. The birds will survive, and they will be back next year. But the squirrels have taken up permanent residence. In any program of this sort it's almost impossible to get rid of Waste, Fraud and Abuse -- particularly Abuse, who is young, hungry and ambitious.