As Richard von Weizsacker gets up from his desk to greet a visitor, he looks half statesman-president, half kid in a candy store. He obviously likes his new job.
The office is temporary, under the tyranny of long-delayed heating repairs that have kept him out of Villa Hammerschmidt, the official presidential residence. But it has cachet, for it was here that the first West German President, Theodor Heuss, sat in those uncertain fledgling years of German democracy. Baron von Weizsacker appreciates the history of it.
Even though he has been President only a month, he is reveling in the chance to speak out on what he terms ''issues of survival.'' It is a chance he has been waiting for for a long time, with a combination (according to Countess Marion von Donhoff, publisher of Die Zeit) of ''pride because he knows his own rank (but) modesty because as a Christian he knows that public applause isn't the final judgment.''
In his career von Weizsacker has had plenty of moral applause but - until recently - far less political applause. He was nominated for the presidency once before, and lost. As a member of the Bundestag he was respected but treated as a political lightweight. As an aristocratic maverick he was always somewhat aloof from his own Christian Democratic (conservative) Party.
It was only in West Berlin, where he wrested the mayoralty away from the perennially ruling Social Democrats three years ago, that the politician von Weizsacker blossomed.
When he began his term, Berliners were talking about the ''ungovernability'' of their city. When he left, political polarization was no longer a modish topic.
The large, sometimes violent demonstrations were past. By means that included both voluntary contracts and evictions, the number of squatter-occupied buildings had dropped from some 160 to fewer than 10.
As mayor, von Weizsacker saw his commission as not only preserving order but also reconciling his diverse constituents, including conservative pensioners, a thriving coun-terculture, and Turkish guest workers. He valued urban life as the fermenter of new ideas and cultural brilliance. He liked Berlin.
Perhaps the best measure of his success in achieving his aims was the grudging compliment of the city's protest Alternative List. In an internal party memorandum when von Weiz-sacker resigned, AL city council members concluded that his government had not been as reactionary as they had feared.
And how does President von Weizsacker expect to operate as a politician in his new, nonpolitical office?
''I have always looked with surprise (at the view that) it's a nonpolitical role,'' he says in English studied at Oxford. ''I do nothing the day long which is not political. It's just a different sort of political activity.''
He continues: ''I am clearly not supposed to make any party politics. I have to see to it that my visits at certain places in the Federal Republic do not in any indirect sense influence a forthcoming local or regional or Lander election. And of course I am not supposed to take part myself in any party struggle in Parliament. That is quite clear.
''But things which I have to say (address) the political questions of the day or the time. People whom I have to speak to speak of course about exactly the same political questions as they do when they talk to me as governing mayor.... The subjects are the same as they are in other more or less general political talk.''
His constitutional tasks fall into three categories, he notes. The first, signing legislation is, so to speak, the only part that is not very political.
The second, representing the foreign policy of West Germany, is not very public but is still very political. ''I am having conversations with practically all German ambassadors leaving Bonn in order to take up new assignments somewhere, ... speaking to all the foreign ambassadors who are here not only when they present credentials, but also in between, and speaking to very many of the guest heads of government or foreign ministers ... and these, as far as the contents of those conversations are concerned, are of course exactly the same as these visitors' talks with the chancellor or foreign minister or party leaders ... with the exception that usually I don't present my experience out of those conversations to the public.''
The President's third task is one close to his heart. He defines it as ''marking a few points which seem to me to be of some importance, long-range importance ... not in the first place to give recipes,... but rather to ask questions, to encourage certain points, perhaps discourage others.... The influence of the president can be higher or deeper than that of any other politician if he has something to say or ask.''
Asking questions comes naturally to this Grenoble- and Gottingen-educated doctor of laws, father of four, and 25-year member of the Synod and Council of the German Evangelical (Lutheran) Church. (He resigned from the council on becoming President so as not to represent any one group of citizens more than any other.)
On his election last spring he specified that he would listen to the yearnings of East Germans as well as those of West Germans. At his inauguration in July he made it clear he would be asking a lot of tough questions about such things as the environment, hunger, war, and peace.
Certainly a large part of President von Weizsacker's scrutiny will fall on Bonn's relations with East Germany and Eastern Europe. He supported detente with East Germany when the Social Democrats initiated it 15 years ago, more than a decade before his own party came to power and embraced detente in 1982. He was the first West Berlin mayor to visit East Germany. Last year he addressed the major church gathering in East Germany called to celebrate the 500th anniversary of Martin Luther - and there were few dry eyes among the assembled worshipers.
In all issues President von Weizsacker may be expected to continue his hallmark preaching of moderation, civility, and reason. Equally, he may be expected to do so with passion.
It's a nice sort of political role to have.