Vice President Bush has made a strategic decision to move early and aggressively for the support of New Right conservative groups, his aides said yesterday, rather than allow Rep. Jack Kemp (R-N.Y.) or any other potential challenger for the 1988 nomination to monopolize that wing of the GOP as a political base.

The strategy -- which those aides concede has risks of alienating some of Bush's past moderate supporters or being depicted as political opportunism -- will get its first crucial test tonight, when Bush is scheduled to be the featured speaker at a Washington testimonial banquet for the late William Loeb, the staunchly conservative publisher of the Manchester (N.H.) Union Leader.

Loeb was scathing in his descriptions of Bush's challenge to Ronald Reagan in the 1980 New Hampshire primary. Some of Bush's longtime allies in Congress have told reporters they cannot understand the vice president's acceptance of the invitation, and Bush aides said they are well aware that he faces a round of media stories comparing his expected praise of Loeb with Loeb's 1980 editorials questioning Bush's honesty, conservatism and political acumen. Among other things, the Loeb editorials called Bush "a spoiled little rich kid" and a man "unfit to be the Republican nominee for president."

But Marlin Fitzwater, Bush's press secretary, said the Loeb testimonial is merely the first of a series of scheduled speeches at New Right organizations, including the American Conservative Union's convention in Washington in January, the National Rifle Association's convention in New Orleans in April and a national Right to Life conference in Denver in June.

"The vice president is a conservative," Fitzwater said. "His voting record in Congress was conservative. His support of the president is both personal and philosophical and we think it appropriate to let everyone know that."

Lee Atwater, a senior consultant to Bush's unannounced presidential campaign, said, "George Bush has been the No. 2 leader of the conservative administration and the conservative movement for the last five years. It is not only appropriate but desirable for him to go speak to fellow Reaganites and fellow-conservatives."

Bush's decision to accept the Loeb dinner keynote role and the other New Right organization invitations was prompted, at least in part, by fears that Kemp was mobilizing those organizations for a possible challenge to Bush in 1988.

In the last three months, the representative from New York has spoken to antiabortion groups in Iowa, Michigan and Texas, to the Religious Roundtable, the American Coalition for Traditional Values and Concerned Women for America.

John Buckley, Kemp's spokesman, said that Kemp has been leading the legislative and political efforts for right-to-life and other New Right issues far longer than Bush. "Bush certainly has his work cut out for him in persuading people in a variety of New Right organizations he is one of them," Buckley said, "but it would make absolute sense for him to do so now, because of the predominance of activist conservatives in the early primary and caucus states."

A Bush strategist, who requested anonymity, said "it would be absolutely ridiculous for Bush to let anybody else muscle in on the ground of who is the natural conservative successor to Reagan. For him to let a year or two go by and let Kemp or somebody else take over that ground would be criminal."

Bush strategists assert that Bush is seen by most conservatives and Republicans as being thoroughly in tune with Reagan's conservatism. In one recent poll by Bush consultant Robert Teeter, an absolute majority of those who said they voted in Republican primaries said Bush would handle women's rights, minorities, the deficit, economic policy, Soviet relations and taxes "pretty much as Ronald Reagan has."

A 44 percent plurality said the same thing about abortion policy, with 18 percent saying Bush would handle the issue "better" than Reagan and an identical 18 percent "not as well" as Reagan, from their point of view.

On the other hand, the same poll indicated some of Bush's image as a moderate challenger to Reagan's policies in the 1980 primaries still persists. Of those polled, 55 percent identified Reagan with some degree of conservatism, 26 percent called him moderate and 10 percent thought him liberal. For Bush, 39 percent of the same voters chose a conservative label, 36 percent moderate and 10 percent liberal.