ALTHOUGH it involves relatively small sums of money, congressional pay is a hot-button issue. The most fail-safe "star wars" system couldn't knock out all the brickbats that will rain on the US Senate for its action last week, when it voted 53 to 45 to raise senators' salaries by $23,200 a year. The raise will bring senators' pay to $125,100, equal to that paid members of the House.For many senators, however, the hike will not result in a net pay increase. In exchange for the heftier paychecks, the lawmakers - in the same tradeoff made by the House in 1989 - renounced honorariums, the fees senators receive for speaking engagements, writing, and other outside activities that trade on their office. Senators have been allowed to pocket honorariums up to $23,068 a year, most of which are paid by special-interest groups. For government ethics, that's a healthy tradeoff. It's far better that lawmakers be beholden entirely to taxpayers for their pay rather than to be hustling speech fees from special interests. (There's still the problem of special-interest clout in campaign financing, however.) But what about the amount of pay itself; is it too high? Certainly many taxpayers will think so - hard-working men and women struggling to raise families on $32,000, retirees thankful for modest pensions. Yet at $125,000 congressional pay is comparable to, even well below, the incomes of many doctors, lawyers, business executives, media stars, labor leaders, and other administrators and decisionmakers (not to mention many athletes and entertainers). The work performed by senators and representatives - who are charged with helping to set policy for and administer the largest enterprise in the world - is at least as important and demanding as that performed by members of these other "elites." We don't begrudge senators the pay, and we applaud the improvement in the ethical climate. OK, let the letters to the editor start flying.