Contemporary American conservatism proclaims itself three generations old. According to its own history, each generation had a task. The first generation's task was just to announce that conservatism exists. William F. Buckley Jr. did that by founding his National Review in 1955. For the second generation, the task was to design political strategies to put a conservative in the White House. It succeeded in 1980. And for the third, it is "to roll back, on all fronts, the liberal conquest of the last half century." The next Supreme Court appointee will make that task easier.

The task of the so-called "Third Generation" is taken from a new book by that name -- a compilation edited by Benjamin Hart of the Heritage Foundation. Its jacket cover is laden with blurbs. One is from Attorney General Edwin Meese III, who writes, "The future is ours." Yet another is from President Reagan, who says, "The greatest days of the Conservative movement lie ahead . . . This so-called 'Third Generation' of conservatives is extraordinarily well-equipped . . . to promote the issues and values that are the bedrock of our movement."

"Our movement"? It's impossible to think of a recent president using those words. But Reagan sees himself as the leader of the conservative movement. He is an ideologue, and the book for which he has supplied a blurb is starkly ideological.

The liberalism that the Second Generation assailed, the Third would shred. Among other things, it would prohibit abortion, restore prayer to the schools, deny homosexuals civil-rights protections, dismantle many, if not most, welfare programs, and -- although this is by no means a consensus -- make divorce harder to obtain.

Sooner or later, some of these issues will be decided by the Supreme Court. With the retirement of Lewis Powell, that court now hangs in the balance. And yet, Democrats in general and those in the Senate in particular shy from saying that they will apply an ideological yardstick to the person Reagan nominates as Powell's successor. For some reason, this most ideological of all presidents, the Godfather of the "Third Generation," is to be treated as if he is not intent on advancing an ideological program. The person he nominates primarily for ideological reasons is supposed to be judged by other criteria.

To many Americans, the word "ideology" seems foreign -- a vaguely European affectation, like drinking tea from a glass. But a glance at what some Third Generation members have in mind will tell you otherwise. There is nothing vague about their ideology. If "the movement" led by Reagan were to have its way, abortion would be banned outright. Rape victims, befuddled 13-year-olds, women carrying fetuses doomed by disease -- all would be denied abortions. Choice, that overused word, would be used no more. The government would make it for you.

Similarly, capital punishment, the American disgrace, would be expanded. The condemned, who now include the mentally feeble, might be expanded to include juveniles as well. Prayer -- not necessarily your own -- might be returned to the schools and the government's power to censor increased.

These are not obscure, abstract issues like a return to the gold standard, but examples of how ideology affects the way you live. Supreme Court appointments are a clear way to implement and maintain an ideology. In fact, they are the only way a politically exhausted Reagan administration -- rebuffed at the polls in 1986 -- can implement and perpetuate its ideology.

There is ample historical precedent for the Senate to reject a nominee on ideological grounds. In fact, one of every five nominees to the court has been rejected by the Senate, some on purely philosophical grounds. In 1930, for example, President Hoover's nomination of federal judge John Parker was rejected because of his too-conservative ideology. And he was rejected by a Republican-controlled Senate.

If Reagan chooses an independent conservative in the Powell mold, the precedent of Senate rejection on the basis of ideology won't be an issue. But if he opts for a movement conservative, as Meese and others would like, then the Senate has the right to judge the nominee on the basis he was chosen -- ideology. As the "Third Generation" knows well, it's what the fight is really about