When Jimmy Carter asked last fall, through an aide, if Prof. Lawrence Klein would become his economics adviser, Klein reacted in a very professorial way: he gave the candidate what amounted to a pop quiz.

Klein sent Carter a number of papers he had written on subjects like unemployment and international trade. Then the two men met last November in New York City. "He had obviously read my stuff and understood it," Klein says. "He is quick to synthesize, and he has a wide range of gut feelings about good and bad economic policies." In other words, Carter passed.

Klein has less happy memories about his service on candidate Eugene McCarthy's economics task force in 1968. "McCarthy did with my work what he did with all his papers: stuck them in his back pocket and said whatever he thought," recalls Klein, who teaches at the University of Pennsylvania's Wharton School. "Before I did anything for Carter I wanted to be sure he was serious."

Klein is so well known in his field of econometrics—which uses mathematical formulas to predict changes in the economy—that he attracts students from as far away as Egypt. He is a meticulous teacher of whom a student once said, "If there are six ways of doing something, he'll want you to do all of them."

The son of an Omaha, Neb., office clerk, Klein, 55, became interested in economics as a boy in the 1930s. "Economic problems loomed very large," he says. "It was a popular subject." Klein was also interested in math, and when he got his degree from the University of California in 1942, he began to specialize in the then new science of econometrics. Considered a liberal among economists, Klein favors a policy of easier money, low interest rates and budgetary prods for the economy. He has drawn up a list of 15 economics campaign issues for Carter—such as inflation, farm income and prices, welfare, housing and consumer protection—defining each and suggesting what the candidate's approach might be. "The fact that we tried to outline a program that is possible," says Klein, "rather than one that is Utopian has made people think that Carter is a conservative. He is not."

Klein studied at MIT, did research at the University of Chicago, taught at Michigan and Oxford before joining the Wharton faculty in 1958. Those years were not without tribulations. In 1945 Klein joined the Communist Party in Chicago when, as he has explained it, party members insisted that he sign up before lecturing to the group on Marxist economics. He remained a party member until he left Chicago in 1947. When the affiliation was revealed during House Un-American Activities Committee hearings in 1954, the University of Michigan denied him an expected promotion. Klein left the country for four years, teaching in England until the Wharton offer came.

Klein is unembarrassed by his Communist background and the McCarthyist aftermath: "It was an act of youthfulness 30 years ago," he says. "I just don't think of those problems now." He maintains contact with Communist economists overseas and in the last year has spoken on econometrics in Poland and the Soviet Union—as well as in Sweden, Greece, Belgium and Japan.

With the presidential campaign approaching, Klein has organized an economics task force of nine members. But so far the pressure has not obliged Klein to suspend his other interests. As president-elect of the American Economic Association, he is planning that group's next convention in Atlantic City in September. He continues to direct Wharton economics forecasts used by government agencies and private industry. Klein's wife, Sonia, an economist he met in Chicago, produces a quarterly survey for Newsweek magazine. The couple has four children, all grown. Not a practicing Jew, Klein is nonetheless "very involved with the state of Israel and other Jewish affairs." (He says he feels comfortable with Carter's firmly held Christian views. "After all the country has been through," Klein says, "it won't hurt us to have a man of religious commitment in the White House.")

Klein is planning now for his fall classes at Wharton and insists he has no interest in a Cabinet post or other government appointment. "I am just an academic giving advice," he says. "If you are a technician and are asked for help, it is a social obligation of citizenship to give it." There are exceptions, Klein admits; he would not, for example, advise Ronald Reagan. "But then," he adds with a smile, "I don't think I would be asked."