On one major foreign policy issue more than on others President Reagan shows potential vulnerability. It is the war-peace issue.
Mr. Reagan says his policies and defense buildup have made the world safer than it was several years ago. Furthermore, the President argues, the Soviet Union has gained no new ground.
His Democratic challenger, Walter Mondale, has consistently responded that the world is less safe: Nuclear weapons talks with the Soviets have collapsed, he says, and a new arms race is under way. Terror threatens the Middle East. In Central America, Mr. Mondale continues, the United States is ''sliding toward war.''
But Reagan has modified his rhetoric over the past few years to the point where, in speeches at least, he places a much greater emphasis on negotiations to resolve conflicts.
Mondale says the ''new Reagan'' is beginning to sound like Walter Mondale. But Reagan-Mondale differences are still obvious, particularly when it comes to dealing with the Soviet Union and Central America.
The Soviet Union. Mondale would invite the Soviets to a summit meeting from the first day that he took office. Reagan proposes a step-by-step approach to summitry, with regular Cabinet-level US-Soviet meetings carefully preparing the way. He opposes a nuclear weapons freeze but now offers tradeoffs of key weapons on both sides to reduce strategic nuclear arms.
The biggest differences between the two men lie not so much in their stated positions as in their often unstated assumptions.
According to one highly placed official, Reagan still believes that the US can get along without arms control agreements.
Defense Department civilians have blocked a number of incipient Reagan administration arms control proposals. In a second Reagan term, as much may depend on whom Reagan keeps in top State and Defense Department jobs as on what his stated positions are.
Central America. The Reagan administration has yet to achieve a negotiated resolution of any major conflict (unless you count the May 17, 1983, Israel-Lebanon accord, which failed to bear fruit). Nowhere is this more apparent than in Central America. The US and nations of the Contadora group seem to be at odds over how to deal with Nicaragua. But Reagan argues in effect that freedom is as important as peace and that with American encouragement democracy is spreading in South and Central America. He favors using the CIA- supported Nicaraguan rebels to keep putting pressure on Nicaragua's San-dinistas. But his advisers are divided as to whether that pressure should extend to trying to overthrow the Sandinista regime.
Differences between the two candidates are much less apparent when it comes to the Middle East and East Asia.
Reagan has modified his old, pro-Taiwan position to the point where previous differences with the Carter-Mondale approach to China have almost disappeared.
In the Mideast, Reagan has swung over the past few years away from mistrust of moderate Arab governments and unalloyed support for Israel to what some observers consider a more balanced view. Reagan opposes moving the United States Embassy from Tel Aviv to Jerusalem.