SINCE THE REPORTS about it were buried in the papers, many readers may not realize that the District of Columbia's home-rule powers are about to be expanded in constructive ways. One of the good things the Senate managed to do in that mad marathon before adjournment was to pass and send to the president - for his expected signature - legislation that has the effect of cutting in half the time that Congress has to review acts approved by the elected local government.

Though at first glance the change may seem minor, the shortening of this waiting time before city-passed legislation can either take effect or die is important on two counts: It is further recognition by Congress of the city government's ability to act responsiblity, and it will bring new order to the local legislative process. The bill sets the time during which Congress may veto a City Council bill at 30 calendar days, excluding weekends, holidays and recesses of more than three days. That's a vast improvement over the old 30-day requirement, which counted only those days when both houses were in session - which could easily come to 60 days.

As Councilman David A. Clarke notes, under the old wording "we had a horrible time trying to estimate when our legislation would take effect." For example, it took seven months for a condominium act to become law. That sort of unpredictablity led the council to enact all too many measures on a temporary 90-day "emergency" basis - a messy way to legislate.

There is another wlcome change in the congressional measure just passed: The bill eliminates authority for the president to veto an action that the council has adopted by a two-thirds vote over the mayor's veto. Though the presidential veto was one of those "protections of the federal interest" that was thought necessary to gain votes for the D.C. Charter in 1973, it, too could have become a serious hindrance to orderly local government. True, the local government remains in check at all times, anyway - for Congress is still free to take back any powers it has delegated to the District. But we prefer to think this latest delegation of authority will lead to still greater recognition that the District can - and should - make the decisions on purely local matters.