DON'T write off President Reagan getting his tax revision enacted - sooner or later - and for reasons that have somehow escaped the heated discussions and varied assessments of the subject.
* Granted, the political battle to enact far-reaching tax reform - a modified ''flat tax'' - will be uphill. Dozens of special-interest groups will fight hard to retain the present progressive income tax code, with all its loopholes and special deductions. A number of key lawmakers, including Robert Packwood, the new chairman of the Senate Finance Committee, are opposed, or have serious reservations. Still, there is broad support from economists - those who identify with liberal Democratic leadership - as well as those who have found themselves fairly comfortable with Reaganomics. They see the reform plan proposed by the US Treasury as one that will bring about badly needed equity.
* The President's political views - the fact that he is both a Republican and a conservative - should make him particularly potent in getting tax revision enacted.
Those who would pay more under the plan are middle-income and higher-income Americans, most of whom were a part of that huge 59 percent majority the President just racked up at the polls. Most lower-income Americans would pay no taxes at all.
So, as Trade Ambassador William Brock was pointing out the other morning, the President now has an opportunity to ''break patterns.'' That is, as Mr. Brock sees it, Mr. Reagan is in a particularly good position to win over those who might feel they were hurt the most by tax revision - simply because they were Reagan supporters, hence, more likely in the end to go along with their President on his plan. ''If Carter had proposed this legislation,'' Brock said, ''it would have been dead in five minutes.''
Reagan's moving toward tax revision is, in fact, a little like President Nixon's opening up the door to relations with Peking and like his negotiating detente with the Soviets. Mr. Nixon's conservative, anticommunist supporters yelped mightily over those moves. But they let him do it, and did not leave his ranks. Why? Because they trusted Nixon not to give too much away to the communists.
Our discussion here presupposes that there is latent support for this federal tax revision plan among the Democrats. There is. Despite dissent from some Democratic congressmen and some labor leaders, there is a widespread view among Democrats - and, if you will, Democratic liberals - that this is a piece of legislation they would have been proud for a Democratic president to father. Example: Massachusetts Democratic Gov. Michael Dukakis praises the Regan tax plan, calling it ''an extraordinary piece of work.''
Robert Dole, the new Senate majority leader, sees tax revision eventually being passed. He thinks all it may need is some ''sweetener'' to satisfy business groups that now feel they would be hurt too much by this plan. Senator Dole says that in the end the ''revenue neutral'' concept in the plan might be dropped - that some deductions might be altered so as to provide revenue and thereby help reduce the budget deficit.
So the upshot seems clear: Don't write off tax revision, despite those who say it is already dead. Ronald Reagan could very well put this legislation on the books.
Godfrey Sperling Jr. is the Monitor's senior Washington columnist.