What tells you much about the plight of Jack Kemp, the leader of the right-wing tax uprising, is where he is looking for sympathy these days. He even went to the president's former favorite punching bag, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

"Now I know," he sighed to Tip shortly after his harsh encounter at the White House, "the woodshed is oval."

Commiseration failed the speaker, as it sometimes does the Irish in the presence of self-pity.

"You ought to know," he responded briskly. "You've measured it often enough."

On the House floor, Kemp sought out Rep. Jim Leach (R-Iowa) who, as chairman of the progressive Ripon Society, is accustomed to pariah-dom.

"I know," he murmured as Kemp, the driven, blow-dry apostle of supply-side economics, told of his discovery of the world of the outcast.

Kemp's ardent advocacy of tax cuts has given him a constituency far beyond his New York congressional district. He was a figure of consequence to Reagan, who in 1980 wooed him warmly and even embraced his theories to get him aboard the presidential campaign.

The current estrangement over the tax bill, which Kemp says the president has assured him is in no way personal, has cast Kemp in an unfamiliar and uncomfortable position.

But if he wants to see supreme awkwardness, he has only to look down the Hill to the White House.

The president is breaking a pick to win over Republicans to a bill that will raise for the hated Treasury $98.9 billion over the next three years. It is the handiwork of another Republican, Sen. Robert J. Dole of Kansas.

Only in April, the president said he had "not come to Washington to raise taxes." He knows it is a rejection of Reaganomics.

He knows that many true believers, and even mainstream Republicans, are willing to "give the guy a chance," as the postman in the nervy Republican Social Security commercial puts it. He is going against "the people who elected him." He is antagonizing the Chamber of Commerce.

As a Reagan intimate mourned, "I have never seen the president swallow as hard as he has swallowed on this one."

It is no wonder, considering the crowding ironies, that the White House has fallen on Kemp as the villain, coloring him as an eaten-alive opportunist who is "using Republicans to further his presidential ambitions."

Kemp, persecuted as he is, does not suffer from a credibility problem. The president, no matter how vigorous his exertions as a tax bill lobbyist, does.

Somehow, it is still hard for some people to picture Reagan, should he fail in his arm-twisting, going out on the campaign trail, looking down at his shoes and saying to an assembly, "Gee, folks, sorry I couldn't raise your taxes this time," without, of course, being able to blame the Democrats.

But apparently this is what haunts him as he hauls in Republican congressmen by the dozen to convince them that cutting back on goodies for the boardrooms is the way to recovery.

Kemp at least is consistent. Nobody doubts that he believes in what he is doing as he undergoes heavy bombardment from Reagan heavies and sniper fire from Reagan staff people. He can say, with some justice, that he is merely trying to save Ronald Reagan from himself, or from the creeping leftism of his counselors, as personified by diabolical James A. Baker III, George Bush's campaign manager.

The White House is conducting raids on the rebel ranks. Obviously it was a matter of minutes to persuade Lyn Nofziger, the unkempt rogue who was long a Reagan hireling, to turn his coat. He came out of the Oval Office, shuffling his feet and grinning and saying he had been "just plain stupid" to take a seat around the guerrilla campfire.

Nofziger's fling with insurrection was regarded in some quarters as the equivalent of taking out a classified ad for his new consulting business.

No one knows how deeply he and the president explored the philosophical nuances of the tax bill during the conversion session.

Nofziger is not known for the inordinate delicacy of his ideological sensibilities, and some speculate that the merest hint that the White House would choke off Republican clients might have been sufficient to induce him to switch teams. Shamelessly lofty, Nofziger said of Kemp, "Jack is hurting the president and the presidency."

To which, rebel Rep. Newt Gingrich (R-Ga.) retorts, "If Kemp went to Argentina tomorrow, we the rebels would go on."

One diverting aspect of the midsummer comedy is that while beating up on Kemp as terminally ambitious, the president's men are ignoring the real author of their anguish, Bob Dole, who seems to have all but announced his presidential candidacy.

Dole has made repeated openings to the left. He has not hesitated to face down the president on voting rights and food stamps. Now he boasts of his tax bill that the reforms "come largely at the expense of corporations and individuals who pay little or no taxes . . . ."

If Reagan is really looking for heretics, Dole's the one.