Like most political towns, Washington is usually a lot more comfortable with custom than with candor. Take the semi-frequent case where a major elected official's performance in office is judged unsatisfactory by the surrounding political community. Our local custom would require that candor be given the afternoon off and that the verdict be partially sealed.

Only partially sealed though, because any observant citizen can learn just when such a negative judgment has been returned on an elected official. Simply listen for repeated criticisms of the officeholder's staff. Of course, when the staff of any officeholder is knocked, the indictment is actually of the officeholder. Any staff is essentially a reflection and an extenison of the principal who formed it.But candor can be dangerous, so it is almost always alleged that good old Dick or Jerry or Jimmy is simply suffering from a staff infection.

Both Haldeman and Ehrlicman, while performing their assigned tasks, lost their first names and their White House mess privileges. Frank Moore and the Georgians were inviting targets of opportunity long before the political community had the nerve to find fault with Jimmy Carter.

With a very few isolated exceptions, President Reagan's staff in the second month of his term is getting good marks. Which, translated, means that Washington's judgment of the president remains positive.

So much for custom; now for a little candor. Every president is entitled to exaggerate in order to dramatize a public situation or to galvanize political support. That's legitimate and to be expected.Reagan has shown himself to be a gifted exaggerator. A couple of million times he told us that he was that rare half-breed, a "citizen-politician," which is presumably less than a citizen but more than a politician. Let us be frank: Ronald Reagan has transformed the Republican Party to his ideology and likeness; Ronald Reagan is an execptionally gifted politician.

What brothers me is not Reagan's business about the rest of us getting off the oil companies' backs, either. That's fine, even if I do refuse to believe, as the president seems to, that there is more oil under second base at Yankee Stadium than all the NATO countries have used since World War II. Now all the controls are off oil; so if the president is right, we should be hearing any day now about our very own equivalent of Britain's North Sea discovery.

No, the real problem is with the buzz phrases that Reagan and Stockman and Meese have taken to using in the presentation of their tax program. Here is one passage from the president's speek to Congress: "The taxing power of government must be used to provide revenues for legitimate government purposes. It must not be used to regulate the economy or bring about social change. We've tried that and surely must be able to see it doesn't work."

As nonsense, that compares with telling a nation of people who are now paying more in income tax than they earned in their second full-time job that the government is today taking a smaller share of the GNP than it did in 1951. "Social Change?" Don't tell a Reagan voter who will never own or rent a tuxedo that tax-deductible tickets to the baroque ball that put the purchaser's picture on the society page are not a form of social change.

Or for that matter, how about the tuition tax credits that the president has promised, along with Rep. Jack Kemp's enterprise zone bill to provide tax incentives for business to invest in depressed areas like the South Bronx? Such proposals, of course, seek both economic and social changes.

Or what about the latest solar-disco promoter in his linoleum cowbody boots? He is free to deduct his business lunch of Dover sole, while our widely beloved blue-collar workers pays for his own BLT.

Of course, every change in the tax law means social change. Let us not consciously deny reality. Some of us may have even begun to believe that Rich Uncle Oscar might know better than Big Brother. But such political baloney about taxes hurts the Reagan case a lot more than it helps.