Washington — Americans will be poorly informed about the candidates' foreign policy views when they go to the polls 12 days from now. Diplomatic experts say that neither President Reagan nor Walter Mondale is shedding light on crucial issues that will confront both the next president and voters, as they are called upon to make intelligent choices. Further, analysts doubt whether the debate this week, or the myriad stump speeches given by the two candidates in recent weeks, have served to enlighten voters.
Assessing the public discourse to date, foreign policy specialists cite, among others, these glaring gaps:
* Mr. Reagan is pushing the idea of an antiballistic missile defense system that in theory would make offensive nuclear weapons obsolete. But he has failed to explain why the Soviets would sit still while the US developed a system that undermined the Soviet deterrent. He says he has ''not round-tabled'' the issue, indicating he has not given it serious study.
Such a system, even if feasible, could not be in place in this century. What does he propose be done in the interim?
* Mr. Mondale proposes a mutual, verifiable nuclear arms freeze. But he does not address the crucial issue of how such a freeze would be verified, given the the Kremlin's penchant for secrecy. Nor does he explain why a comprehensive freeze agreement would be any simpler to achieve than step-by-step accords in specific arms areas.
* Neither candidate has addressed the fundamental problems in the Middle East. The public discussion has revolved around who is responsible for the lapse in security at the US Embassy and the Marine compound in Beirut. But virtually no attention is given to what American policy should be, what has been learned from the Lebanon experience, how to break the deadlock over the occupied West Bank, or how to invigorate the Reagan peace initiative of 1982.
Instead of dealing with the substance of issues, foreign policy analysts say, the candidates have resorted to sloganeering, simplistic themes, and imagemaking. Mondale seeks to present himself as an arms controller, but as a ''tough'' one. Reagan continues to infuse his speeches with optimism, giving the impression that there are no serious problems.
''You're not coming down to the great issues but to whether Mondale is soft on defense and whether Reagan falls asleep in meetings,'' says Charles W. Maynes , editor of Foreign Policy magazine.
Former Undersecretary of State George Ball, characterizing the recent debate as a ''dreary performance,'' comments: ''They spent an awful lot of time discussing the nits and lice, and not getting at the fundamental questions.'' The issue they should have concentrated on, he says, was ''how the superpowers are going to stop the nuclear spiral.''
Campaigns necessarily put contraints on candidates. In the effort to woo critical constituencies, candidates avoid politically sensitive subjects. Thus, Mondale and Reagan both proclaim their fervent support of Israel and shy from saying anything about a Mideast peace effort, which might imply criticism of the Zionist state and thereby alienate Jewish voters.
Yet most diplomatic observers predict an enormous challenge to American diplomacy in the Mideast in the next four years. They see Soviet influence increasing in the region and Israel's power declining relative to its Arab neighbors. Unless there is progress toward resolving the Arab-Israeli conflict, experts say, Israel may one day find itself in a debilitating war of attrition. The US could even be drawn into a confrontation with Moscow.
The failure to articulate a conceptual framework of foreign policy especially concerns many foreign policy professionals. If Americans cannot be expected to understand the complex details of every diplomatic issue, say experts, they at least should have some notion of US objectives in the world.
''What the public ought to get is some larger view and vision of our role in the world and what we want to achieve,'' says Robert Bowie, who served several administrations in high foreign policy posts. ''Our policy has two aspects: One is containment of the Soviet Union; and the other is to try to create some international order outside the Soviet Union. But we have totally neglected the whole positive side of our policy - to create relationships among the noncommunist nations, including the allies and the LDCs (less-developed countries).''
It is not unusual for presidential campaigns to neglect serious foreign policy discussion. But analysts recall some campaigns that actually helped educate the American electorate and made a difference in the long run. In 1956, for example, Adlai E. Stevenson appealed for an end of nuclear testing in the atmosphere. He lost the election, but the idea was later realized in the Limited Test Ban Treaty.
Other questions that beg public discussion, experts say, are whether the US can live with a Marxist government in Nicaragua as long as it does not export revolution; how to cope with the impact on the US of staggering population growth in Latin America; and how to manage the US relationship with the USSR at a time when the latter's power is on the decline.
''Mondale has not brought out the range of issues well in the campaign,'' says Lincoln Bloomfield, a political science professor at the Massachusetts Institute of Technology. ''And Reagan is a wild card in terms of what he'll do in a second term. So this is not a campaign on the issues.''