Standard Oil is buying the Kennecott Copper company. Standard of California is buying another metal company, Amax. Mobil is still digesting Montgomery Ward and Exxon is still figuring out what to do with Reliance Electric, Conoco, Gulf and Occidential have all bought major coal companies.

So what? So nothing from this corner in the way of a moralistic blast at the big, bad oil companies. But their acquisitive habit does raise doubts about the supply-side economics so dear to the Reagan administration. It even suggests that, maybe, taxes on the oil companies should be raised.

The economic policies of the administration center on the claim that money moved from the public to the private sector will be invested to improve output and productivity in ways that reduce shortages, diminish inflation and promote full employment. As a test for that theory, the oil companies are first in line.

Thanks to deregulation and the shortages of 1974 and 1979, the oil companies are flush. Texaco, Mobil and Standard of California hold over $3 billion apiece in cash or the equivalent. Standard of Ohio, Standard of Indiana, Gulf of Phillips have nearly $2 billion apiece.

The special competence of the companies bears a close relations to the national interest. What the companies are supposed to do best is find, extract, transport, refine and sell oil and gas. The United States and its allies are so short of petroleum that American foreign policy sometimes gets made in Saudi Arabia, Libya and Nigeria.

Practically to the point of pledging, furthermore, oil company executives said they would plow increased revenues back into discovery. At least that was the line when they were trying to get the Congress to decontrol oil back in 1979, and dilute the windfall profits tax.

Alton Whitehouse, the chairman of Ohio Standard, testified to the Senate Finance Committee on July 12, 1979, that " . . . the surest investment our country can make in the short term . . . is to emphasize traditional oil and gas exploration. We will get the biggest bang for our buck on that program."

J. Dennis Bonney, of Standard of California, when asked what the company would do with windfall profits, told the Senate Judiciary Committee on June 25, 1979, that "our preference, our strong preference, would be to reapply those profits to reinvestment in the oil and gas business . . ."

Jack Allen, a spokesman for the independent producers, testifying on deregulation, told a House subcommittee on energy and power on May 16, 1979. that "the increased revenue resulting from this program would have been recycled into exploration and drilling, as has occurred all during the history of the petroleum industry. . . ."

Drilling, to be sure, is now at record levels, but the companies have money left over that they are not putting into oil and gas exploration. They are spending tidy sums just to buy off the present stockholders of companies that are in many cases good and efficient and don't need any help.

Nobody can blame the oil companies. They are making sound investments. Metal companies, in particular, have been depressed because of environmental regulations in this country and expropriation dangers abroad. Both perils are now receding, so the oil companies are getting into good things, and assuring bigger returns to their stockholders. But the fact is that making money available for investment to private companies doesn't always work to promote the public good. Sometimes there's a difference between national interest and corporate interest. The difference emerges when the oil companies spend revenues, which the country though would yeild more energy, on mere financial deals.

It is not only the private sector, moreover, that invests for the future. Money spent by government on defense and education and health and highways and housing is also an investment in the future. So is money spent by government on programs that avert civil strife. If the government is short of funds, if it has to pinch in areas that hurt the whole society badly, then it makes sense to look for additioanl revenues. One place from which the public sector can probably draw more money without doing great harm is the oil industry.

In the present national mood, of course, a rise in oil company taxes isn't likely. But a large point is germane. The play of free market forces does not by itself inevitably promote the national welfare. The market has to be made for the common good -- by thoughtful government policy.