When President Reagan deep-sixed moderate Republican John R. Evans, who had served 10 useful years on the Securities and Exchange Commission, and nominated conservative Republican Charles C. Cox, he did more than abandon a known talent for a man who gets poor ratings from other commission members.

This shortsighted exercise was the latest evidence, as consumer advocate Ralph Nader says, that Reagan is a "corporatist," not a mere conservative. According to Nader, a "corporatist" is one who responds to what the elitist element in corporate society wants done, whereas the conservative merely follows the dictates of a cautious ideology.

Nader insists that the only time Reagan ever challenged the corporatist position was when he initially banned exports of equipment for the Soviet gas pipeline. On that issue, Reagan's anti- communist passion temporarily overrode his corporatism instincts. But guided by Secretary of State George Shultz, Reagan soon went back to traditional establishment thinking.

In my view, the establishment viewpoint on supplying equipment for the gas pipeline happened to be the right one, considering the impact Reagan's original position banning sales would have had on the European economy-- and, ultimately, on U.S.-Soviet relations.

Nor can I go along with Nader's opposition to larger appropriations for the International Monetary Fund. The overarching need in this case is to avert a global depression, even if in doing so a few big banks are saved from the effects of their own irresponsible loan policies.

Nader is on sounder ground when he limits himself to domestic issues. It is clear that throughout his public career Reagan has knee-jerked to the corporatist line. For example, the president shows no interest in a vigorous enforcement of the antitrust laws. He has either been oblivious to or condoned mergers (Congress hasn't done any better) while morale in the government's antitrust offices has dwindled.

On the other hand, conservatives usually favor the antitrust laws to restrict monopoly, and to allow free markets to operate.

For Reagan (and some of his key aides), devotion to free markets has been mostly a matter of rhetoric. Big business--agri- or industrial--is favored over small business. The Reagan tax cut was heavily slanted to the upper-income brackets and to large corporations. Consumer protection counts for little. Yet, because Reagan's pro-corporate pitch is disguised as "conservative," there has been remarkably little criticism from genuine Republican conservatives or liberal Democrats.

Reagan supports subsidies for nuclear power and synthetic fuels (opposed by the National Taxpayers Union), while withholding the same generous hand for solar energy and conservation.

Reagan's personal business friends have more infuence than presidential advisers such as Economic Council member William Niskanen, or former CEA Chairman Murray Weidenbaum. They opposed Alaskan pipeline legislation which guarantees the participating consortium against risk. Reagan's pipeline stance ensures higher natural gas prices for homeowners.

Despite solid conservative backing for the protection of America's public lands, Reagan has opened the wilderness and the environment to new threats. If it's the meat industry versus consumer standards, Reagan is with the meat industry. (Also, watch for meat import quotas later this year.)

Similarly, if it's Detroit against consumers on auto safety standards or air bags, Reagan lines up with Detroit-- although conservatives like George F. Will are breaking with him on this issue. Will has come to understand that accident prevention can reduce enormous taxpayer costs for medical care, rehabilitaton, etc. That's the true conservative position.

In summary, then, sound conservative doctrine accepts the use of the government's police power in the health and safety arenas, just as it supports the antitrust laws to police the marketplace against predatory pricing.

In the SEC-Evans case, Reagan did exactly what the big boys in Wall Street wanted: he got rid of a dedicated commissioner who had challenged their absolute power, while seeking to protect stockholders. Cox, who has no securities industry--or even business --experience, was handpicked by SEC Chairman John S. R. Shad a year ago to be chief economist for the commission.

The remaining commissioners--Republicans and Democrats--fear that Cox was sold to Reagan by Shad, because the chairman wants a rubber stamp to help carry out his intention for rapid and too extensive deregulation of the securities industry.

It shouldn't be too hard for Congress to take a good look at the reasons behind the dumping of Evans and at Cox's qualifications. It would be a healthy exercise, and might put at least a temporary brake on corporate power.