Over 25 percent of the viewing audience in the major cities watched the presidential debate in Baltimore. Ronald Reagan and John Anderson held the audience for the second half hour. So the debate was a significant political event.

It almost certainly helped both Reagan and Anderson. Jimmy Carter now has to get back on the board. Which means facing up to problem he has so far ducked -- the Anderson problem.

Reagan emerged from the Baltimore debate once again as the master of the nation pieties. I have heard or watched his three-minute closer on the special destiny of America five times previously. It still strikes me as the best political television I have ever seen.

No doubt some of Reagan's simplistic comments hurt him with educated voters. "I notice," he said at one point in the debate, "that everyone who is for abortion has already been born." That's not going to play well in Scarsdale or Shaker Heights or Marin County or any of the other middle-class residential suburbs.

Still, on the big issues -- on inflation, on energy and on defense -- Reagan sounded reassuring. While he may have been wrong, he certainly didn't seem wild. Among Democrats leaning to Reagan in the South, and in the industrial centers of the Middle West, his position has probably been enhanced. He got his across to his people.

Anderson showed himself to be highly articulate, penetrating in analysis and a full master of the facts. He also demonstrated, in his response on the abortion question, a passion many people had not previously sensed. More important, on the big issues, he drew the policy lines between himself, on the one hand, and Reagan and Carter, on the other.

With respect to the economy, he pointed out that Reagan (and Carter) favor a big tax cut beginning in January of next year. That cut would come on top of a $60 billion deficit. It is bound to be inflationary. In contrast, Anderson prefers to hold up on tax cuts until he gets government spending under control. Even then he would link the bait of tax reduction to price and wage restraint by business and labor.

With respect to defense, he showed that Reagan (and Carter) favored big, expensive boondoggles -- the MX missile and the B1 bomber respectively. Anderson is more discriminating. He reserves his spending for pay increases, a bigger Navy and readiness forces that give a military payoff in the areas that count.

The basic similarity between Carter and Reagan on the major issues plays a critical role in the next stage of the campaign. For the question now is how Jimmy Carter will arrange to go one-on-one against Reagan.

The president may be even in the national popularity polls, or even slightly ahead. But because of Reagan's solid base in the western states, Carter still lags badly in the electoral college. The more so if, as seems likely, Anderson is cutting into Carter's strength in the major eastern states. Furthermore, Carter may have recently hurt himself badly by the show of a mean, petty streak in implying Reagan was a racist. So the president wants badly to debate Reagan head-to-head. He wants to show that he is master of the facts and Reagan an ignoramus. He wants to set his own experience and calm against the suspicion that Reagan may put a hasty finger on the nuclear button. He wants to show that he can be as engaging personally as the former governor of California.

But there is a lion in the path of a Carter-Reagan debate. Reagan has repeadtedly insisted that he would encounter Carter only if Carter agreed to take on Anderson. The Reagan camp is now asserting that position with renewed firmness. So Carter faces a hard choice. If he wants a shot at Reagan, he will have to agree either to a threesome or to a subsequent debate between him and Anderson.

Both are bad news for the president. Both dilute the up-or-down choice between him and Reagan that he seeks to push upon the electorate.

So it can be said with confidence that the loser in Baltimore was Jimmy Carter. He could have joined the three-way debate and brushed Anderson aside. Now he has to face up to Anderson directly with lines drawn, and at a time closer to the election. He has to pay, in other words, for the cynical attitude he has always shown toward public dialogue.