LAST MONTH, the Commission on Executive, Legislative and Judicial Salaries recommended tying salary increases for top officials - including members of Congress - to a strong code of public conduct. And we warmly applauded the concept. Since then, House Speaker Thomas P. O'Neill Jr. has vowed to give the House "the strongest code of ethics of any constitutional legislative body in America." Today, if the Democrats in the House are serious about moving in this direction, they should vote against the reappointment of Rep. Robert L. F. Sikes (D-Fla.) as chairman of the House Appropriations subcommittee on military construction.

To award a porkbarrell job to a member who was formally and resoundingly reprimanded by his colleagues last year for misconduct - failing to report to the House his ownership of stock in Fairchild Industries and holding an interest in a bank that he helped get established at the Pensacola Naval Air Station - is to make a mockery of the whole House effort to raise both the compensation and the standards of conduct expected of public servants at the highest levels.

As the salaries commission suggested, public trust in government is so low that members of Congress cannot increase their own salaries without running a substantial risk of being thrown out of office at the next election. Moreover, said the commission, "If we continue down the path of the past eight years, in which the politics of survival have required no pay raises at all, we must accept the implications of a government of only the rich, or only the young and untried, or more likely, a government of those who are willing to compromise themselves with political money. The costs of such a government reach beyond the costs of a salary increase; they are incalculable, and to a free people unacceptable." Commission chairman Peter G. Peterson, in an article in the Wall Street Journal, argued further that it is futile to propose salary increases "unless the leaders of the other branches of government join the President in a tangible commitment to major reform."

So today's vote on Mr. Sikes is more than a mere internal party-organization decision. It is a sharp test of the House Democrats' attitude toward the hard part of the ethics business: the strict and consistent enforcement of standards. Mr O'Neill and Majority Leader Jim Wright have tended to be "forgiving" toward Mr. Sikes, which is understandable if you accept the old congressioanl ways of doing business. At least Mr. O'Neill is now saying that he is "not trying to influence the caucus one way or the other" on the vote. Members who believe that codes of conduct ought to be enforced should take Mr. O'Neill at his word on this point. Since the Speaker doesn't seem to care one way or the other, they should feel wonderfully free to reject the bid by Mr. Sikes to retain a special position of trust that he in no way deserves.