ON NOVEMBER 18, 1975, the Federal Election Commission issued an advisory opinion allowing Sun Oil Co. to form a political action committee for the purpose of collecting money from its employes and distributing the money to candidates for political office. In the intervening nine years, PACs have become the bogeymen of American politics.

The SunPAC decision set off an explosion in the growth of PACs, especially among corporations. At the time there were about 700 PACs; by the end of last year there were about 3,500. During that period, the number of corporate PACs grew by 1,600 percent. Labor PACs, which ironically helped to spawn this development in campaign financing, grew by 88 percent.

In the past decade, PACs burrowed into the political life of Washington. By 1982, PAC contributions accounted for more than 30 percent of the money raised by candidates for the House of Representatives and 18 percent of the money given to candidates for the Senate. PAC money has become such a foundation of the American political system that even some PAC managers now complain that members of Congress and senators badger them for contributions. One PAC official says Sen. Pete Wilson (R-Calif.) asked for a $5,000 contribution in early 1983 -- not to retire his 1982 debt, but to prepare for his 1988 reelection contest!

The proliferation of PACs brought with it an unresolved debate: Do these institutions corrupt the political process? Larry J. Sabato, a professor of government at the University of Virginia and author of an excellent earlier book on political consultants, answers with an equivocal "no." PAC Power, Sabato's fourth book, is a dispassionatedescription of the origins and habits of PACs, an informative sourcebook for those interested in how PACs do their business. Sabato is not out to get PACs. Indeed, he occasionally goes out of his way to make them look respectable.

Still, the picture he paints is often worrisome. On the key question of whether PAC contributions buy votes in Congress, Sabato cites a number of studies linking votes in Congress to PAC contributions -- dairy price supports is one example, the House veto of the Federal Trade Commission's so-called "lemon rule" on used cars being another. But he argues that "these occasions are not nearly as frequent as anti-PAC spokesmen, even congressmen themselves, often suggest."

Sabato's bottom line on the issue of whether PACs have corrupted the process is summed up this way: "Whatever the degree of contemporary corruption caused by PAC money, it pales by comparison to conditions prevailing before the Federal Election Campaign Act and the amendments of the 1970s. If contributions of $5,000 (the maximum allowable for PACs) are thought to buy congressional votes, then the Capitol must have been a covered market in the days when groups could make contributions" many times that size. "It is ludicrously naive to contend that PAC money never influences congressmen's decisions, but it is irredeemably cynical to believe that PACs always, or even usually, push the voting buttons in Congress."

SABATO examines a number of proposed reforms. He opposes limiting the amount of PAC money a candidate can accept, saying this would help incumbents and wealthy candidates and is probably unconstitutional. Furthermore, he says, it would promote independent expenditures by PACs, a development that he sees as most disturbing. As a way of diminishing the influence of PACs, he favors raising the limits on individual contributions to candidates from $1,000 to account for the inflation that has taken place since the law was enacted. And he argues that the 50 percent tax credit for donations to candidates should be raised to 100 percent. He would limit the credit, however, to contributions made to House and Senate candidates from the contributor's own state or to political parties. Gifts to PACs, would no longer qualify for a tax credit.

If there is an evil influence in the PAC world, at least in Sabato's eyes, it is the "nonconnected" or ideological PACs, the fastest-growing subspecies in recent years. These are best typified by the National Conservative Political Action Committee, or NCPAC, which made its reputation a few years ago attacking, sometimes inaccurately, Democratic candidates. In 1980, NCPAC helped defeat such liberal Democratic senators as George McGovern, John Culver and Frank Church. Noting that independent expenditures by these PACs are often "viciously negative in tone," Sabato writes that "it is hardly something the system of campaign finance should encourage."

Overall, however, Sabato is content to let PACs continue to operate much as they do today. He approvingly quotes Martin Franks of the Democratic Congressional Campaign Committee, who said, "Those who think they're going to limit special interest money are hopelessly naive, and they may end up doing just the opposite. I've lost faith in our ability to actually reform the process."