IF YOU HAVE trouble feeling sorry for anyone who makes more than a million dollars a year and is a megawatt celebrity, perhaps you should not read on.

I warn you because I am about to express my sympathy for Tom Brokaw, who, I scarcely need tell you, anchors the NBC Nightly News with Roger Mudd.

Brokaw is catching it from right and left for expressing opinions -- not, mind you, on the air, but to a periodical. Both Joseph Sobran, who doesn't agree with him, and Colman McCarthy, who does, have written sternly critical columns about him. They both earn their living by opinionating, which is an absolute no-no for Brokaw, and they think he broke the newscaster's code by giving for print some thoughts which, caught by the network, would cost him his job.

Maybe the subliminal problem for them is that they think that people who earn either $2 million (Sobran says) or

.2 million (according to McCarthy) should not let down his hair to a magazine which kicks the stuffing out of the establishment. Perhaps his tax bracket should talk to Fortune in its off- hours.

Brokaw is literally "a limousine liberal" -- he is taken to and from work in a chauffeur- driven car -- and possibly his choice of a left- wing monthly was to send a flare to his colleagues (notorious progressives, predominantly) that he is still one of them, or at least that he hasn't given up thinking.

And why should he? The most common complaint about his kind is that they are a dry-blown, mindless lot who can do no more than "rip and read."

The rather pompous precede to the interview says that Brokaw, yearning "to be more than a television icon," wants "to be respected for his ideas and his intelligence."

Well, Mother Jones' interview may not do that for him. What he says will not dazzle with its originality or depth. It is superficial and trite, the standard, everyday, left-of-center complaint about the Reagan revolution. He finds the Reagan approach to government "pretty simplistic," which is something not likely to knock his 16 million viewers out of their lounge chairs.

Yet Colman McCarthy sees Brokaw's "scattershot venting" as a grave lapse "that can't help eating into the public trust of the media." Sobran, on the other hand, finds Brokaw's approach as "simplistic" as Reagan's.

It isn't as if, on duty, he comes on as one of those "raised eyebrow cynics" who sent Spiro Agnew into his famous frenzy about "nattering nabobs of negativism." I have studied his boyish face to see if are any physiognomic signals to hint that that he thinks the news he has just read about the economic recovery or the president's latest solution for El Salvador may be just a bunch of stuff. I see none. To me, he is a model of impassivity, as compared, say, with Charles Kuralt, whose face and voice both noticeably droop when he recounts massacres, mass rapes and other breaches of civility.

Even so, Joseph Sobran concludes from the Mother Jones evidence that Brokaw "seems to think that his job is to expose the flaws in our society from a mildly leftist perspective . . ."

Colman McCarthy approvingly recounts the contrasting demeanor of another anchorman, Frank Reynolds of ABC, with whom he once dined.

"Even in relaxed company, in off-the- record conversation, Reynolds wasn't trading in opinions about the events he was paid to cover as a reporter." I like to think that Reynolds just didn't feel like talking shop that night. But McCarthy implies that his work has made him a kind of high priest of our society, one who takes a vow of mental celibacy which applies not only to the moments when he is performing the solemn rite of reading the day's events off the teleprompter to the nation.

I wonder if there is ever a time or a place when such an awesome figure is permitted freedom of expression. I have been musing about what might ensue when Mrs. Brokaw asks him, of an evening, what kind of a day he had.

Would the proper reply be: "My dear, it was a mixed day, with good aspects and bad. The tape machine broke, the line to Beirut went dead and we muffed the lead on monetary policy. But lunch was excellent and the sixth floor liked the show. All in all, I feel that Roger and I can be content that we brought to the American people a balanced, objective and impartial account of what transpired in the world today."

And if he should find himself next to Colman McCarthy or Joseph Sobran, I trust that should either seek to divine what he really thinks about our policy in Nicaragua, he will either smoothly deflect the discussion to the weather or simply say, with the loftiness required of his eminence, "I can't comment on that."