IF CONGRESS WERE a private company, its employment practices might very well land it in deep trouble with the law. The latest study, for the House Administrative Review Commission, shows the extent to which discriminatory patterns persist. White men still hold most of the top staff positions in the House. Women who do have high-level jobs are likely to be paid less than men doing comparable work. Blacks constitute only 6.8 per cent of the House work force and are concentrated in the lowest-paying jobs. The scene in the Senate is much the same. Moreover, most of the 20,000 or so Capitol Hill employees may be hired and fired arbitrarily and have no protection against unfair treatment.

Congress is not deliberately unfair, Rep. David Obey (D-Wis.) said the other day; it's just that the House "reflects society." Not quite.Employment policies in most parts of society are improving, far more quickly than on the Hill - and partly because of the fair-employment laws that Congress has applied to nearly everyong except itself. What those surveys really reflect is an institution that feels no particular obligation to practice what it legislates. Thus, while both houses have passed antidiscrimination rules, the old habits of patronage and typecasting of workers remain strong in many offices.

To an extent, Congress ought to be different and autonomous. The independence of the legislative branch could easily be undermined if federal civilrights agencies got involved in policing congressional personnel practices. By the same token, each senator and representative needs the flexibility to organize his office as he sees fit and to hire people who are politically and personally compatible. That does not mean, however, that congressional employees should be treated uncivilly or regarded as having no rights. And it is hard to see how legitimate flexibility would be undercut by, for instance, guaranteeing equal pay for equal work, or requiring each office to spell out its own policies, so workers would at least know what to expect.

The House commission and the Senate Governmental Affairs Committee are now trying to devise fairemployment programs that take into account Congress's unique sensitivities and organizational sprawl. The handling of employees' grievances is a ticky business, given legislators' demonstrated reluctance to police one another's conduct.The House commission is considering a conciliation process that would be better than nothing. To enlarge job opportunities for women and members of minority groups, both panels are concentrating on affirmative but non-compulsory efforts such as on-the-job training and broader recruitment of professional staff. Surely Congress is ready for that. Indeed, it's hard to see how any legislator could object - if only because, as perceptive politicians, they ought to know that their personnel practices are embarrassingly out of date.