AFTER IDLING in neutral for most of the running of the General Assembly in Annapolis, Gov. Harry Hughes has suddenly slammed into high gear for the last lap with a call for higher taxes on gasoline and trucks. More than a few lawmakers are claiming political whiplash. The governor should not have taken this long to get his tax act together. Some members of the legislature may like to call it thoughtfulness, but to most it was indecision, and it could cost him.

Given the budget-butchering orgy going on in the State House these days, it's a wonder any of the lawmakers even heard the governor's announcement. It could not have been more poorly timed: while opponents as well as would-be supporters of tax increases are doing frenzied austerity dances all over the budget, here comes the governor out of hiding to suggest more taxes. Still, if there are members in attendance with any vision, they should rally to this better-late-than-never call and work out a formula that can be enacted.

As we noted here more than a month ago, Sen. Laurence Levitan (D-Montgomery) suggested early in the session a modest gasoline-tax compromise that at least would help to cover some of the spending that Gov. Hughes is proposing. The Hughes request, in fact, is a stiffer version of the Levitan plan. The senator had proposed that the senator has proposed that the gasoline tax be based on the average wholesale price per gallon of unleaded gasoline; instead of the current flat charge of 9 cents a gallon, 10 percent of the average annual wholesale price would be charged -- with a maximum increase of one penny a gallon each year. The Hughes version would double the cap to 2 cents for 1982 and then lower it to a penny in future years.

Somewhere in this math lies a politically realistic and financially sound formula that could and should be approved before adjournment. But time is short and Gov. Hughes will have to move a lot faster and more forcefully than he has so far if he is serious about winning approval of a sound tax package.