How you score the second and final presidential forum depends on what you think an election is all about, and what criteria are used. For the partisan-minded, Mr. Reagan came through the Kansas City event with a show of the familiar ease with an audience, humor, and composure for counterattack missing from his debate performance two weeks ago. His GOP supporters can feel reassured their campaign is again on track. They can resume their basic game plan for the last two weeks of the campaign. Mr. Mondale's backers can likewise claim that their candidate again showed a conceptual grasp of the issues that contrasts with his opponent's more instinctual approach. He continued to assure independents and nominal Democrats of his competence as a leader, which he must do to further narrow the gap between the President and him.
The second forum basically enhanced trends and themes already in place. Mr. Mondale attacked the President on issues of competence, mastery of detail, and accountability for decisions. The measure of leadership should be toughness tempered by wisdom. Mondale tried to outflank the President by constant reference to strength. Mr. Reagan responded by charging that the Mondale record on arms control and foreign policy was one of unilateral disarmament and weakness. ''I know it will come as a surprise to Mr. Mondale,'' he said at one point, ''but I am in charge.'' In this wrestling to pin the one as being too weak and the other as too uninvolved, the outcome appeared a draw. In the polls, Reagan has consistently been holding in the mid-50-percent range; it has been Mondale's rating that has moved upward of late. For Mondale to win, the President would have to make a significant mistake to dip below 50 percent, and he did not do that Sunday night.
If an election is viewed less as a choice between two candidates or two parties and more as a process of voter decision - a time when the public reviews national policy broadly and in some detail - the debates were a help. Mr. Reagan deserves credit for agreeing to the process, as President Carter did in 1980. Mr. Mondale rightly thanked the President for taking him on in 1984.
The voters now have a better sense of disagreements over the ''star wars'' defense program - which President Reagan describes in visionary terms as one day making offensive nuclear arms obsolete, and which Walter Mondale sees as destabilizing to the current arms picture because the Soviets could view the defensive system as implying a first-strike threat. The same can be said of the issue of immigration control along the southern US border: We know better where the lines of dispute lie.
On the question of terrorism and national humiliation, the comparison has been drawn between the seizure of American hostages in Tehran during President Carter's term and the series of terrorist attacks on American installations in Beirut. Mondale asserts that events in Central America - CIA-backed subversive attacks on Nicaragua, or the new flap over a CIA guerrilla manual for the anti-Sandinista contras - have ''spent a good deal of America's assets'' in credibility abroad. Mr. Reagan counters that the Soviets moved against Afghanistan during the Carter-Mondale, not the Reagan-Bush, administration.
The President's strongest argument in foreign affairs is that America is now, relatively speaking, at peace. This is akin to his advantage on prosperity. Mr. Mondale can highlight the administration's lapses, the tardiness of direct contacts with the Soviet leadership, the lack of apparent progress on arms control, and so forth. The President himself opened the question of competence with his faltering performance in the first debate. But America's lack of an immediate international crisis gives the President an advantage that appears not subject to debate.
The exchange regrettably focused more on the pursuit of national strength than on achieving an equal and parallel exercise of moral and diplomatic energy in pursuit of international peace. In his four-minute summation, Mr. Reagan related how a person a hundred years from now, driving along the California coast, would know whether ''we used those weapons or not.'' Again, however, the emphasis was more on stating peaceful intentions than on mobilizing to broaden the conditions for harmony among nations.
Now it's back to the public, to render the final election judgment.