THE CONGRESSIONAL controversies over regulation of members' outside earnings show how times have changed. Serving in Congress used to be a part-time job. Members convened here for a few months and then went back to their professions and businesses. Private income was essential and viewed as generally legitimate. Illegal arrangements were dealt with case by case, if at all.

Now, serving in Congress has become a year-round job. Official pay and allowances are so ample after the latest pay raise to $57,500 that members don't get very far pleading financial hardship as justification for making money on the side. At the same time, the potential for conflicts of interest and public concern about ethical problems have increased dramatically. And the presumption has been reversed: outside earned income has come to be widely viewed as suspect and exploitative.

We would not push that presumption too far by requiring members of Congress to sever all financial ties with the private enterprises from which they come. Top executive-branch officials and judges are expected to give up outside earnings while in public service, but a legislator's relationship with the private world is more complex. It could be healthy for a congressman to work in a hardware store back home on Saturday or carry out an old commitment to administer a small estate for a family friend. That is different from trading on one's incumbency or getting fat fees for little work from someone seeking access and friendliness on Capitol Hill.

In theory, the best remedy is detailed, public financial disclosure, strictly enforced. That should deter the most flagrant and embarrassing abuses. It would also inform voters and help them exercise the ultimate discipline at the polls. Indeed, Congress has grown more willing to undergo that scrutiny; full public disclosure, fiercely resisted not so long ago, is now regarded as necessary or at least inveitable.

In practice, though, this remedy tends to work only in competitive districts and states. Some legislators are so entrenched that they could disclose a $100,000 "consulting fee" from a defense contractor and get re-elected anyway. One might reply: So what? Don't voters have the liberty to elect scoundrels to Congress if they wish? Of course they do - but improper conduct by any member also clouds the Congress as a whole. Thus Congress also has the power as well as the obligation to impose some institutional self-discipline.

Both houses have already put limits on honoraria. The pending ethics codes would tighten those curbs and restrict total outside earned income to 15 per cent of a member's official salary. This is not a perfect approach. We are not troubled so much by the fact that earned income and investment income would be treated differently; that complaint is effectively answered, it seems to us, in an article by Rep. Lee H. Hamilton (D-Ind.) on opposite page today. What does give us some pause is the assumption that impropriety can be determined by the dollar amounts involved. In fact, $2,000 in "legal fees" might be more corrupting than, let's say, $10,000 for teaching at a university.

Yet limits do help by proscribing huge fees from any single source, and keeping members' outside earnings in some reasonable proportion to official salaries. This is not just good for appearances' sake - although appearances do matter, especially when you consider the current image of Congress. It is also good for removing the temptation to engage in richly remunerative activities that would present conflicts of interest. Even with limits, members would still be free, if they choose, to accept modest payment for outside work that does not conflict with congressional business. This, in our view, is more equitable and workable than barring certain categories for work (such as legal practice) entirely, or trying to define by law every one of the blatant or subtle conflicts that cause concern. No code of conduct will eliminate corruption or the need for careful judgments by legislators and voters. The rules now being advanced in both houses will, however, help Congress discipline itself and assure the public that members intend to treat their high office as a full-time job, free of conflict with whatever they may find time to do on the side.