I don't know what President Reagan will hear when he meets with allied leaders in Ottawa in a week, but I suspect the talks won't convey the full tale of what lies beneath the troubled state of the Western alliance. They couldn't, because the most critical voices will not be heard there.

That is the impression left from separate conferences here and in Berlin of groups of about three dozen European parliamentarians, politicins, educators and journalists and their American counterparts. At those meetings of the Aspen Institute Berlin and the Atlantic Association of Young Political Leaders, we heard the following things, not all of them mutually consistent:

1. There is a growing potential of crisis within the alliance, keyed to the deepening doubts in Europe about the wisdom of American policy and the prudence of seeking security primarily through military efforts to deter the Soviet nuclear threat. The skepticism is most evident among younger people -- the so-called "Successor Generation" to those now in power, who inherited their leadership from the original architects of the postwar alliance. It centers now on the question of deploying medium-range nuclear missiles in Europe while delaying ams talks with Russia, but it represents deep currents of religious as well as political belief and can be ignored only at peril.

2. At root, some say, the challenge is cultural and generational. It reflects the young Europeans' boredom with the Cold War and the suspicion that it is a relic of their parents' fixation.

Or it represents a failure of permissive education systems on both sides of the Atlantic to impart the lessons of history to these youths. A German professor sees it as a healthy reaction in Freudian terms, a necessary revolt against the "father figure," Uncle Sam. A French politician says it represents the ambivalence of the young about the values of materialism, the very concept of progress. In any event, the argument is not between the United States and Europe but between the generations.

3. Alternatively, at root the problem is economic. "We have our internal Ss20s," a Frenchman says, referring to the Soviet missiles targeted on Western Europe. "They are called inflation and unemployment." A British Tory MP reports that unemployed youths in Liverpool mix "ban-the-bomb" shouts with their imprecations aginst the bosses and the cops. A German says that young people feel that just as their governments have lost control of their economies, they will lose control of the weapons they are eager to build. A countryman asserts that unions fear that Reagan's "reverse redistribution" policies may be adopted as the model for Europe. In any case, a veteran American diplomat says, the threats of trade wars or oil-access rivalries dwarf the differences over military strategy.

4. Some would like to believe the problem is Russia. What is shaking Europe, they say, is nothing more complicated than naked fear -- fear engendered by the realization that the Soviets have upset the military balance in their own favor and now have the capacity to reduce Europe's cities to smoking ruins. Others think the Soviets are shrewdly manipulating European opinion by promoting the "peace" movements and by propagandizing in ways that suggest they are "reasonable" and the Americans intransigent on arms control.

5. Many assert the problem is not anti-Americanism but anti-Reaganism. Some of them are honest enough to concede that six months ago, they would have used Jimmy Carter's name instead of Reagan's. But despite the differences in the policies and personalities of the two presidents, they see a common denominator: an uncertain, ill-defined approach to foreign policy, symptomized by sudden swerves of policy. To them, Reagan represents high interest rates, minimization of human rights concerns, an effort to drag the Third World into the Cold War arean and a slowdown if not an outright sabotage of nuclear arms negotiations. "The answer to anti-Americanism," says a Dutch parliamentarian, "must be found in America."

6. If there is a problem, others assert, it is no one's "fault." Nations must operate their foreign policies on the basis of interests, not sentiments, and in some areas, Europe's and the United States' interests just diverge. Europe has profited from trade with the Eastern bloc since the beginning of detente, and is understandably more reluctant to see it end. Europe has its own economic and political links to the Arab nations and the Third World in general. It cannot accept that Nato must function as monolithically in regard to those countries as it does toward Russia. The alliance will be all right, these Europeans maintain, so long as there is tolerance for the inevitable differences that will arise among allies.

7. Finally, there are a few who say the whole "problem" is a fantasy, a concoction of Soviet propaganda, or a few alarmists, or a European press some of whose members may be projecting their own hostility to the United States. All three parties in Germany -- a focus of the current concern -- espouse the alliance as the keystone of their foreign policy, a German diplomat calmingly declares. Opinion polls show the United States still by far the most admired foreign country.

In France, where anti-Americanism is nothing new, the recent campaigns were singularly devoid of such expressions, a French jounalist contends, and President Mitterrand has given the mildest of rebukes to American criticism of his appointment of Communist Cabinet members -- an impertinence which no U.S. president would tolerate from an ally. As for England, the Thatcher government is eagerly buying Trident missile submarines, and the best known names in the Labor Party broke ranks rather than accept the left-wing "unilateralism" of those now in the ascendancy. So what's to worry? The "Dutch disease" -- the possible rejection of new "theater nuclear forces" -- can hardly infect all of Europe.

After listening to this talk fill the Junior Common Room at St. Peter's College here, or the villa that Aspen has built on the lakeside site of Joseph Goebbels' former residence, one can grow more than a bit confused.

But the most dangerous court for American policy-makers, I came away believing, would be to accept the last view, the counsel of those who say there is no cause for concern. I say that because the most urgent voices -- the most critical and passionate -- were those of the politicians in their 30s, and they are the ones best qualified to point where Europe may be headed in the future.

It is clear that the tensions which made a John J. McCloy say, "I have never been as concerned about the alliance as I am today," are at least in part generational in their origins and expression. "Every sixth-former [16-to-19-year-old] I meet is wearing a CND [Committee for Nuclear Disarmament] button," Chris Patten, a British Tory MP, said at lunch. His colleague, David Hunt, a defense specialist in Parliament, told the conference here that the young people in his Merseyside district "are agnostic, antistructuralist, almost anarchic in their views and responsive only to broad sentiments like 'peace.' I'll go to a meeting of young blacks in Liverpool 8, where youth unemployment is about 36 percent, and in the middle of talking about jobs, they'll say, 'Oh, by the way, when are we going to get rid of the nukes?' It seems like an irrelevancy to me, but to them, 'nukes' are part of the 'arrangement' of society that they reject."

At the Berlin meeting, Jakob Kohnstamm, a 30-year-old newly elected member of the Dutch Parliament, said, "Anti-Americanism is not the problem; it's really more of an international generation gap. We don't see government bringing the economic solutions we want and there is fear that nuclear deterrence is creating its own problems.We all agree that the Ss20s are a threat, but we think it is ridiculous to build up our destructive power to the point we can kill every Russian three or four times."

"Do you and your friends ever talk about Hitler's exploitation of the military imbalance?" one of the older conferees asked in a sharp tone.

"The balance of power is not irrelevant," Kohnstamm replied disdainfully. "But being able to kill a person once is enough. Why should I have the power to kill him three or four times?"

As that exchange indicated, even in the artificially polite atmosphere of the conference rooms, far from the demonstrations or the amplified oratory of the antinuclear rallies, like the church-sponsored Kirchestage that drew more than 100,000 people, many of them youths, to Hamburg late last month, there was a real edge to the generational exchanges.

When Karlheinz Schonauer, the paid executive director of the youth wing of Germany's ruling Social Democratic Party, joined the Berlin conference, the atmosphere changed. The young Socialists had just repudiated Chancellor Schmidt's policy of commitment to 1983 deployment of medium-range missiles in Europe. Schonauer arrived just as McCloy was warning that "anti-Americanism in Europe" could trigger a go-it-along response in Congress and the administration.

"It's not anti-U.S.," Schonauer corrected the American, who is old enough to be his grandfather, "it's anti-U.S. policy. You speak of 'the free world,' but there are very different interpretations of that phrase. Alexander Haig's view on right-wing regimes makes some young people think that if his policy had been in effect 40 years ago, the U.S. would have been allied with Hitler instead of opposing him.The medium-range missile raises the spectacle of a 'winnable' nuclear war being fought in Western Europe. Many, many of our young people are afraid of that, and their fear feeds the new peace movement."

The older generation of Germans -- diplomats, politicians, professors -- were pained, incensed, embarrassed by Schonauer's words. "My party is trying to teach history to our young people," said one Free Democratic member of the Bundestag, with an expression that suggested, "You see what we are up against."

But what they are really up against is the passage of time. World War II, the Marshall Plan, the NATO alliance, the Berlin airlift, even the Berlin Wall -- a few miles away -- were all before the young people's time.

As Karsten Voigt, a predecessor of Schonauer in the youth job who is now a sometimes critical young supporter of Schmidt in the Bundestag, said, "It is important to understand what lies behind the alienation of our youth. You cannot expect young Catholics to support U.S. policy in El Salvador. You cannot expect young Protestants to support his [reagan's] policy in South Africa. You cannot expect our environmentalists to applaud James Watt, or our trade unionists to praise the cutbacks in social programs in the U.S. We need the freedom to try to influence each other, without condemning each other as we do it."

A member of Schmidt's government, who may not be identified by name, said toward the end of the Berlin meeting that "my impression is that the interdependence of Germany, Europe and the U.S. is much more complicated and critical than I had realized. There are such changes taking place that we cannot afford to take things for granted."

And here at Oxford, a few days later, David Hunt, the mid-thirtyish Tory MP, said, "I hear all this concern about the 'Successor Generation.' I'd guess I'm what they're talking about. And I want to tell you, there's a lot smaller gap between me and the generation now in power than there is between me and the young people I meet when I go home to Liverpool -- the ones in their 20s. If the policies were hard to explain to us, think what it's going to be like to explain them to them."