More than 300,000 retired federal and postal workers who now get the minimum $122 per month Social Security benefit would lose part of it under proposals cleared by the Senate Budge Committee and Senate Finance Committee.

Congress established the idea of a minimum Social Security benefit years ago. Currently about three million Americans get the $122 payment even though their "wage histories" -- the time they were covered by Social Security, their salaries and the money they paid into the system -- entitle them to less than the mimimum payment of $122 per month.

Both committees and the Regan administration want to slash millions of dollars in Social Security payouts by limiting people to the amount due them. Retirees would not lose their entitlement to Social Security. But they would lose entitlement to the full amount of the minimum monthly benefit.

The Ways and Means Committee (it handles Social Security matters on the House side of the Congress) also favors elimination of the minimum benefit. But with an important difference. Key members on the House side would allow the three million retirees -- including about 350,000 former government workers -- to kep getting the minimum. They would eliminate it only for persons who become eligible in the future for Social Security payments.

The House version strikes many people as fairer, since it would not cut the check of anyone drawing Social Security now. It is also politically safer. It is an almost sure thing that Congress will eliminate the minimum benefit. The question -- to be decided by the Senate-House conferees further down the road -- is whether to make the change prospective, or retroactive.