AMERICAN voters are of two minds in this postwar summer.Ask them about President Bush, their commander in chief, and they cheer. Mr. Bush is the only Republican president in 12 years to enjoy equal approval among men and women. But ask voters how America is doing overall, and they boo. Since January, pollsters have recorded a steady increase in the number of people who believe the United States is going in the wrong direction. The latest assessment of the American mood comes from Richard Wirthlin, who once did polling for Ronald Reagan's White House. Dr. Wirthlin doesn't visit the White House as often these days; he supported Sen. Robert Dole (R) of Kansas for the presidency in 1988. Wirthlin's conclusions are supported by a recent ABC/Washington Post survey, which showed an approval rating for Mr. Bush of 76 percent among both men and women. The president's support in the Wirthlin poll was 75 percent among men, 74 percent among women, a difference considered statistically insignificant. At a breakfast meeting with reporters, Wirthlin noted that Bush's image, once fuzzy, has "very strongly crystalized" following the Gulf war. The Gulf crisis gave voters an understanding of the president they never had before, he says. Women were particularly impressed that the war was waged with few American casualties, Wirthlin says. Foreign policy crises always boost a president's image for at least three or four months, Wirthlin observes. But this war was more than an ordinary event for most voters. It firmed their attitudes. Now Bush has become the first president in nearly 30 years to get an approval rating of more than 70 percent for more than six months in a row. The White House staff could take a holiday - except for one thing. Ever since the first of the year, growing numbers of voters believe the country is running amok. In January, 32 percent said the country was on the wrong track, Wirthlin reports. Those numbers have gone up every month, and by June 17-19, when Wirthlin took his latest nationwide survey of 1,000 people, 56 percent felt the country was on the wrong track. Why? Apparently domestic concerns are becoming more important. While Bush focuses on foreign policy - from the Soviet Union's economic crisis to South African apartheid - voters are far more troubled about what's going on at home. Specifically, people are worried about social issues, like homelessness, poverty, hunger, health-care costs, drugs, pollution, education, and crime. Some 41 percent say these are the nation's No. 1 problems. Others fret about pocketbook issues, like the year-old recession, unemployment, the federal deficit, inflation, government spending, and high taxes. About 34 percent of the people list those as top issues. Foreign policy, on which Bush spends most of his time, is a top priority to only 5 percent of the voters. Although domestic issues appear to give Democrats a political opportunity, there isn't much in Wirthlin's survey to cheer them up. For example, 55 percent of the American people now identify themselves as conservatives, among whom Republicans have their greatest appeal. At the same time, 41 percent of the voters now identify themselves as Republicans, while only 40 percent of them say they are Democrats. Even so, opportunities exist for the Democrats. If the increasingly conservative US Supreme Court overturns Roe v. Wade, the 1973 decision which established the constitutional right to an abortion, it could hurt Bush among young people. At the moment, the president's strongest support comes from persons 18- to 24-years-old (81 percent) and 25- to 34-years-old (80 percent). Yet it is those same groups that most vigorously favor abortion rights. Should the court act before the 1992 election, the president's coalition could begin to weaken.