"Aren't we a very old team?" Winston Churchill asked Prime Minister Neville Chamberlain on Sept. 2, 1939, surveying Chamberlain's proposed war Cabinet. It is a question President-elect Reagan also should ponder as he begins Cabinet-making in earnest.

In fact, he should broaden the question: Aren't we in danger of becoming a very old, very gray and very establishment team of businessmen with reputations as managers but not as men of ideas? Before Reagan himself has made a single Cabinet decision, the most probable and important selections are arousing anxiety among his supporters.

The antidote happens to be very old himself but is anything but gray, is not establishment, not a businessman, not a manager and is surely filled with ideas: Ronald Wilson Reagan. Just as Reagan is the best hope for radical economic and national security policies, he is also the principal obstacle to an old Gray Cabinet.

That Cabinet is taking shape in leaks from senior Reagan aides, New York lawyer William Casey, 67, at CIA and Los Angeles lawyer William French Smith, 63, at the Justice Department are considered all but certain. Those twin executives from the Bechtel Corp., Casper Weinberger, 63, and George Shultz, 60, are prime possibilities to be named somewhere -- State Department, Pentagon or Office of Management and Budget.

Adding William Simon, at 54 neither old nor gray, only slightly modifies the gerontocracy of this presumptive Cabinet. Along with Reagan, soon to be 70, its average age is almost 63. That approaches the proposed Chamberlain war Cabinet's average age of 64 ("Only one year short of the old age pension!" the then 65-year-old Churchill exclaimed).

But age is not the most serious problem. Some insiders call it an "embarrassment" to maked an attorney general out of Smith, described by one Reagan adviser as "a society lawyer." Reaganites blame him, as Reagan's family lawyer, for Reagan's politically embarrassing zero income tax payments of the past. Whether such criticism is well-founded, nobody has accused Smith of serious thought about government.

Nor does anyone believe that Casey, a brilliant World War II manager of espionage operations, has an agenda for rehabilitating today's CIA. Although Weinberger may return to his Nixon administration post at OMB, his transition paper on the budget is considered by experts to be 10 years out of date.

The widely respected Shultz is so much an establishment conformist that even some of his admirers believe he would be an effective secretary of state only in an administration peppered with younger, more innovative personalities. oOtherwise, he might take on the coloration of his older, grayer colleagues.

Why are the names emerging from Reagan's kitchen cabinet so lacking in youth, dynamism and imagination? Because the advisers, elder establishmentarians from the world of business, seek above all managerial ability.

Past Republican administrations, as well as Jimmy Carter's have been reduced by the notion that managerial ability is the principal governmental skill. Lawyer-banker Laurence H. Silberman, a trenchant Republican analyst of government, has written that ideology and program are far more important. Without ideology, Silberman wrote in 1978, "we see the now familiar picture of President Carter pondering each new question as if it were an isolated ad hoc engineering problem."

That is why the abrasive, controversial Simon is welcome relief to Reagan supporters who worry about an old gray Cabinet. Whatever the complaints about his temperament, Bill Simon lives in the world of ideas. What's more, he is willing to change them, currently showing much more inclination toward radical supply-side economic notions.

Republicans originally attracted to Reagan as a force for change also want at least one young, clearly innovative figure in an important Cabinet post. Rep. David Stockman of Michigan, 34, carries that hope in an intensifying push for him as OMB director. Stockman has informed Reagan transition agents he has no interest in a token position, such as secretary of energy.

The conventional wisdom doubts Reagan would stray far from the advice of his old friends. While insisting on massive tax cuts and massive defense spending against the counsels of cautions, it might be too much for Reagan to cast a gimlet eye on eminently-respectable recommendations from his kitchen cabinet.

But unlike those retired business tycoons, Ronald Reagan has never met a payroll. For the last 20 years, he has dealt with ideas -- showing startling receptivity to new concepts. He might prefer a few younger colleagues with similar intellectual boldness by his side.