'WHAT do you think of the Senate's pay raise?"For most passers-by in downtown Washington, D.C., last Friday afternoon, the answer was "What pay raise?" Suzanne, a public information specialist for a broadcast network, was indignant. "You mean the Senate wants to raise its pay again?" she asked. It just did, she was informed - late last Wednesday night, after the evening news, after most journalists had gone home, and with no advance public warning. In a surprise appropriations-bill amendment introduced by Democratic and Republican leaders, the Senate voted 53 to 45 to raise its pay by $23,200, bringing salaries up to those of House members - $125,100 a year. In exchange, senators agreed to a ban on honorariums for speaking engagements. To keep any opposition from mobilizing, Senate leaders orchestrated the move in secret, consulting their colleagues and striking as soon as they thought they had the votes to carry it off. By the weekend, the issue had disappeared from the news media. But for the nation's 100 senators, the fear is that the issue will not vanish for good. "It's electoral dynamite," says Steve Schier, a professor of political science at Carleton College and author of the forthcoming book "Congress: Games and Strategies." "The question for many of these guys is, 'Is this going to turn into a campaign ad against them? he says. Professor Schier says the pay-raise legislation, which must be approved by the House of Representatives and signed by President Bush, is a good idea because it helps eliminate the financial pressures that have led some senators to accept speaking fees from companies or organizations trying to influence legislation. "It boils down to this: Senators will now get their extra money from the taxpayers instead of special-interest groups," says Schier. But consumer advocate Ralph Nader immediately decried the large salary boost as unseemly in light of the nation's financial troubles. IN the end it will be the voters who pass judgment on the move. And it appeared to be no coincidence that of the 33 senators who will be up for reelection in 1992, 25 voted against the pay hike. Though some Senate proponents of the salary increase have claimed that the House raised its pay two years ago without negative consequences at the polls last November, at least one former congressman disagrees. In a letter Friday to the Washington Post, former Rep. Jim Bates (D) of California wrote that at least three representatives lost because of the pay raise: himself, Doug Bosco (D) of California, and Doug Walgren (D) of Pennsylvania. "It may not have been the only issue, but our polling and our opponents' polls rated the pay raise the No. 1 issue," Mr. Bates wrote. "Most incumbents did not have seriously funded opposition. But in most competitive races, it was a big issue." In 1988, a presidential commission recommended salary increases for all three branches of government in an attempt to take away some of the political liability of a decision to raise pay. The House of Representatives raised its salaries by $28,500 and banned honorariums last January, but the Senate got cold feet and voted for only a $3,500 cost-of-living increase. The Senate's last big pay raise was in 1987, when salaries jumped up by $12,100. The aim of the presidential commission was to make federal salaries comparable to those of top-level nonprofit executives with the hopes of attracting more talent to government jobs. In the Senate, some members expressed concern that the expense of being a senator would keep all but the most wealthy from seeking a seat. Most Americans probably would have a hard time relating to a family that has trouble making ends meet when its annual income is more than $100,000. But for some senators, that is exactly the case. If you're unmarried, have no dependents, and happen to represent a state near the District of Columbia and can therefore get away with having only one residence, then life as a senator can be fairly inexpensive. But there is no such senator. Most do maintain two residences, pay taxes in two jurisdictions, have dependents to support, two wardrobes - and, some, tuitions to pay. Some senators say they will contribute the increase to charity or social causes. That's exactly what Karen Jackson of Montpelier, Vt., hopes for from one of her senators, Democrat Patrick Leahy, who supported the pay hike and faces reelection next year. Ms. Jackson says she'll probably still vote for Mr. Leahy, because of his support for abortion rights, but she plans to write him an angry letter. "My support group for mothers of sexually abused children had to stop meeting because funding ran out," says Ms. Jackson, in Washington on vacation. Senator Leahy "can contribute to that." She also points out that her family of four, including a son in college, lives on only a little more per year than the amount of the Senate pay raise.