THE IDEA that has haunted big business for decades-that bigness is, by definition, badness-is now squarely before Congress in a politically explosive setting. Sen. Edward M. Kennedy put it there this week by introducing legislation to bar the 16 largest oil companies from acquiring any company with assets greater than $100 million.

The political appeal of the senator's proposal is clear. The oil companies are fair game these days, and public sentiment is strongly in favor of congressional action that appears to penalize them. This legislation seems to do that by cutting off their ability to buy up companies in other lines of business with whatever profits they reap from the decontrol of oil prices.

If these profits are as large as Sen. Kennedy and others think they are going to be, the problem this legislation addresses may be a real one. A company with an extra billion dollars in its treasury has to do something with it. It can pay the money out in dividends to its stockholders or it can enlarge its own operations through expansion or acquisition. The senator's proposal eliminates most of the last option. If it had been in effect, it would have barred the recent acquisitions of Montgomery Ward by one oil company and of Anaconda by another.

General legislation that would have forbidden acquisitions like these was porposed earlier thie year by Mr. Kennedy, the Department of Justice and the Federal Trade Commission. It would limit the kind of acquisitions or mergers possible for all large companies. By coming up with a version of the same idea aimed only at oil companies, Sen. Kennedy focused the issue in the way that is most helpful to his cause. While there is little public support for letting the oil companies get rich off the energy crisis, there is even less for letting them move into other industries because of it.

The senator's new initiative may well divide the solid opposition that the business community has presented to the earlier proposals. Some big businessmen may see this as an opportunity to divert to an attack on the oil companies the effort that is being made to win passage of broader legislation. Others may see it as the foot-in-the-door for limitations on the size of all corporations.

The new proposal, however, presents only a variation on the basic question raised by the broader legislation. It is whether the country-for economic, political or social reasons-wants to put a leash on the ability of corporations to become larger. This question has been raised repeatedly during the last hundred years, perhaps most notably in the early years of this century when Louis Brandeis made his impassioned pleas against big business. Now that it has been cast in terms of an industry that is under attack for other reasons, Congress may have to answer it.