Washington — Finally it's over. The lame-duck session of the Senate that has been called an ''ordeal'' and a mistake and the ''laughing stock'' of the country went home for Christmas after crushing a filibuster and passing a 5-cent gasoline tax hike.
Much maligned on virtually all sides, the post-election session nonetheless leaves the nation an important legacy. It pushed through a major transportation bill in a little less than four weeks, raising some $27.5 billion over the next five years.
A small band of conservatives, led by Sen. Jesse Helms (R) of North Carolina, fought the proposal by every legislative tactic available, on the principle that they opposed raising taxes. But in the end, while Senator Helms kept his colleagues up several nights and delayed their trips home for Christmas, he won little except enmity on the Senate floor.
The lawmakers seemed more impressed by hopes that the bill would provide money to build and repair the nation's ''crumbling'' highway and mass transit systems, as well as provide some 300,000 jobs.
But such issues faded into the background in the lame-duck session as senators watched Senator Helms, with help from fellow North Carolina Republican John P. East, tie up the entire body.
Senator Helms's relentless opposition also poses problems for the Republican leadership. Despite pleas from the President, who favored the gas tax legislation, the North Carolinian refused to give in.
The problem is the ''ideological split'' within the Republican Party, said Sen. William S. Cohen (R) of Maine, at a press breakfast this week. The problem will increase in the coming year as 19 Republican senators prepare for reelection bids. If ''moderates see no discipline in the conservatives of the party,'' said Senator Cohen, then they cannot be expected to follow behind the President either.
In rare personal attacks, Democrats accused Helms, who is chairman of the Senate Agriculture Committee, of making enemies for farm interests. And Sen. Edward M. Kennedy (D) of Massachusetts suggested in a floor speech that Helms be stripped of his chairmanship.
The Helms-East filibuster has produced a throng of calls for reforming Senate rules that give every member almost unlimited power to stop action. Even after the required 60 senators have voted to limit debate, a determined minority can continue to filibuster through amendments. Several senators are now calling for a rule to end such ''post-cloture'' debates.
The events of the past weeks will almost certainly set the scene for a reform movement in the next Congress.
As for the impact of the gas tax measure, beginning next April motorists will pay an additional nickel a gallon in federal taxes for gasoline and diesel fuels. The new tax, charged at the refinery and added to the current 4-cent tax, will cost the average American an estimated $30 a year.
Truckers will pay higher fees for using the nation's highways, with maximum rates going from $1,600 per truck in 1984 to $1,900 after 1988. And the industry will also pay higher excise fees on new trucks and tires.
Meanwhile, Congress attached several unrelated ''Christmas tree'' amendments to the bill. It extended unemployment benefits to some 2 million recipients whose payments are due to run out this spring. And as a gift to American ship owners, it allowed Americans who attend professional conventions aboard US-registered cruse ships to deduct expenses from their income taxes.
As a gesture to labor, the bill also has a ''buy America'' ingredient that requires most concrete, steel, and vehicles purchased through the act to be at least partly made in America.