For six months now, the criticism of the man has been as inconsistent as it has been insistent. Take your pick: he is either a hopeless liberal, out of touch with the times, or he is too quick to cave in to, or cooperate with, the conservative opposition. He should go on television more often, it is said. But when he does, he is reminded that he is neither as charismatic as Ed McMahon nor as articulate as Brent Musburger.

He has been called too old and too heavy, and you know that some of the knocks have to hurt. But not once, in a recent interview, did the speaker of the House complain about any of the cirticism. Tip O'Neill, for anyone who may hav noticed, is a certified professional.

O'Neill believes that the judgment on how well he has led the Democratic House will be delivered on Nov. 2, 1982, the date of the congressional elections. As for now, he is confident that his actions, this sessions, have been in the best interest of both the nation and his party. And the speaker can make a pretty good case for his confidence.

Nobody can accuse House Democrats of being obstructionists. House Democrats fought hard, if mostly unsuccessfully, to protect their traditional constituencies from the Reagan budget cuts. Tip O'Neil promised Ronald Reagan that there would be an up-or-down vote on his economic recovery program before the August break. The professional's word is not lightly given.

O'Neill genuinely admires effective and strong political leadership -- the kind that the president displayed in defeating the Democrats in the House on taxes and budget. Says the Democratic speaker of the Republican president: "You have to respect someone who can produce. He has employed the tools available to him very, very well."

He did not mention that his own tools are severely limited. The speaker has no federal appointments to mention, no White House dinner invitations to extend, not even a pair of semi-official cufflinks with which to woo his colleagues. The contemporary speaker must rely exclusively on other tools -- his own personal persuasiveness, his friendships, his reputation for integrity and effectiveness. That's about it.

During the last administration, O'Neil had the ostensible support of a Democratic White House in lining up votes. During the Carter presidency, there were 23 separate House votes on budget resolutions. On those votes, on average of 63 House Democrats voted every time against their speaker and their president. It can be said of Tip O'Neil in 1981 that he cut in half the number of defections among Democrats -- only 29 on the crucial budget vote.

Regularly, the speaker is urged to punish those Democrats who do vote with the president. O'Neil knows from painful personal experience what it means to be out of step with his party. In 1967, O'Neill became the first regular big-city House Democrat to break with Lyndon Johnson over Vietnam. rAs he noted this week, "We Democrats have always been the party of dissent. How are we supposed to distinguish between dissent and disloyalty?"

That's a legitimate question. And one that should be answered by those on the speaker's ideological left. They may wish to reflect on what it might have been like in the mid-1980s if such party discipline and punishment had been in force. The congressional hearings that made respectable and debatable the opposition to the Johnson policies were the product of an unorthodox Democrat -- Sen. J. William Fulbright.

Tip O'Neill is not unqualified in his praise of the president. Pointing out that the entire Reagan tax message is quite short of any calls to sacrifice, the speaker said: "The three-year tax cut is not exactly the hardest thing in the world to sell."

To be with O'Neil for any period of time is to be guaranteed interruptions for phone calls. These were the calls that he has been making and taking for 50 years. To a young woman whose mother had died, there was comfort. To a former colleague just out of surgery, there was a quip and a compliment to the friend's wife -- "it was a lucky corner he turned, Eileen, the day he met you." The talk was of family and jobs and death and politics.

But all of them were very personal, full of first names and reminiscences. You had to wonder if all the media condidates with the capped smiles and the blow-dry look have the time to make such calls.

The thing about this speaker is that he actually believes his favorite quote from the late Hubert Humphrey: "The moral test of government is how it treats those who are in the dawn of life, the children; those who are in the twilight of life, the aged; and those who are in the shadows of life, the sick, the needy and the handicapped."

The speaker is a professional and he cares about his craft. He should not be undersestimated.