Rushing to bash President Bush as a ''liar'' for employing the ''T'' word, his political and media attackers missed the real target: White House bungling in failing to anticipate both the political storm certain to follow written use of the word ''tax'' and the predictable fury of antitax Republicans.

However the low comedy of the budget summit finally plays out, last Tuesday's presidential statement can no more support the charge of ''liar'' than Bush's decision last month to convene the budget summit. As we wrote then, ''a higher-taxes, lower-spending budget deal with Congress'' and a ''backing away from'' the no-tax pledge were the clear messages of the decision to take the deficit problem to a bipartisan budget summit.

In the face of that, calling Bush a ''liar'' for Tuesday's statement is a bum rap. The question is not presidential veracity. It is whether, on the heels of the first killer storm in his still-young presidency, the kinder, gentler chief executive can gain control of the chaotic budget process, reduce the deficit close to Gramm-Rudman dimensions and tickle the Federal Reserve Board into a bit of easing.

That means persuading exultant Democrats to do what the Tuesday statement implied. Composed on the spot in longhand by Budget Director Richard Darman and White House Chief of Staff John Sununu during the president's session with bipartisan leaders, it said Bush and Democratic congressional leaders agreed that ''entitlement and mandatory program reform'' are ''require{d}.'' Thus, the word ''tax'' was designed to guarantee that the Democrats are indeed required to use the spending-cut axe in hitherto off-limits terrain.

As for Bush, he must hold the line against tinkering with the personal income tax ''bubble'' or raising any other tax rates. The ''bubble'' lifts the personal income tax rate from 28 percent to 33 percent for individual incomes between $47,000 and $90,000 a year, then reduces it back to 28 percent.

For a White House that prides itself on the cerebral power and political clout with which Sununu and Darman perform their daily business, the failure to anticipate the tornadic political and press reaction to Bush's use of the ''T'' word is strange. It is ''the biggest single mistake'' of the Bush presidency, Republican House whip Newt Gingrich, a conservative anti-tax stalwart, told us.

Gingrich did not mean the statement per se. He meant the obliging way it was worded, as if its purpose were to invite attack by Bush's critics, both protax liberals and antitax conservatives. He meant the failure of the White House to consult beforehand with Republican antitax leaders like himself (he learned about it from CNN). He meant phrasing that could be construed as saying exactly what Sen. George Mitchell, the Senate majority leader, boasted when he rushed out of the White House to tell reporters that Bush ''has concluded that tax increases are necessary.''

Some Republicans remain suspicious about Bush's tax plans, despite the lack of solid evidence of any conspiracy theory. The suspicion centers on doughty Dick Darman, the submerged and crafty infighter who is suspected by one key Republican political leader off Capitol Hill of plotting removal of the ''bubble'' by nailing in a new top marginal rate. The suspected rate would be 33 percent, and it would apply to all income for individuals over $47,000.

But Darman is too shrewd not to know a few facts about the antitax Republican right. Among these conservatives in the president's party are some rank-and-filers who have long been determined to undermine Bush's presidency as unprincipled and pragmatic. They now view his newly alleged apostasy on the tax issue as the final straw.

If the president did embrace Democratic demands to raise the marginal income tax rate to, say, 33 percent, and if so staunch a party leader as Gingrich decided to fight the change, Darman knows his president might lose between 100 and 110 Republican votes in the House. That would be a devastating blow to presidential authority and a dark apparition for 1992.

But such decisions lie far down the track of the budget summit. Chances of obtaining essential spending-cut breakthroughs and the vital reduction in the 28 percent capital gains tax before the congressional election are slim to none. The time to judge whether Bush has really violated his pledge is after the budget stalemate ends weeks or months from now.