WASHINGTON (AP) _ Pro-choice Republicans said Wednesday that blunt rhetoric from President Bush opposing changes to federal abortion restrictions only strengthens their resolve to change the GOP's antiabortion stance, even if it means a divisive election-year platform fight.

Bush's tough rhetoric came in a warning to Congress that a veto awaits any attempts to change existing abortion financing and counseling regulations.

''Given the importance of this issue, I am writing to make sure there is no misunderstanding of my views or convictions,'' Bush said in his letter.

The president's willingness to make, unsolicited, a toughly worded statement of his antiabortion views was interpreted by some pro-choice GOP activists as a sign he has no plans to moderate his stance - or the party's - heading into his expected 1992 reelection bid. But other GOP activists disagreed with that view and said a compromise that would avoid a nasty platform fight was possible.

Pro-choice forces in the GOP found it ironic Bush sent the letter the same day a Democrat won a special congressional election in Massachusetts in which the Republican candidate's antiabortion views were a major issue.

''It seems to me that the message from voters is loud and clear but the White House isn't listening,'' said Mary Dent Crisp, chairwoman of the National Republican Coalition for Choice. ''The majority of voters are pro- choice.''

Another pro-choice GOP activist was more optimistic, saying she recently received indications from the White House that it was willing to discuss compromise platform language.

''It might not be the perfect language but I think we may see a step in the right direction,'' said Ann Stone, who heads the Republicans for Choice political action committee. ''If not, we're organizing and will be ready to take our case to the convention delegates.''

The pro-choice party factions hope to elect supporters to the GOP platform committee at the 1992 convention and also to flood the committee with testimony espousing a platform change. Republican National Committee Chairman Clayton Yeutter has said he does not want to change the platform.

''There's going to be a big struggle, no question,'' Crisp said.

The next chance for the pro-choice forces to make their case is an RNC meeting later this month in Houston. But no resolutions dealing with abortion were introduced by the deadline. Stone said her group planned ''extensive groundwork'' at the meeting but would not be more specific.

Several party leaders and operatives said they expected considerable discussion of abortion and the political impact of recent court decisions at the meeting, but not in public sessions.

''It's certainly fair to say there is a potential problem for us,'' one GOP leader said privately. ''But we probably won't know how big of a problem until we get into 1992 and see what else the court has done and what happens in the Congress.''

Several Republican strategists played down the political impact of an internal party fight over abortion, noting similar debates in 1984 and 1988 did not keep Ronald Reagan and Bush from winning the White House.

''Abortion is always an issue, but usually in presidential campaigns it doesn't turn out to be a very decisive issue,'' said prominent Republican strategist Charles Black.

Others, however, said abortion could prove a more potent presidential issue in 1992 because of Supreme Court decisions since 1988 that have made it easier for states to restrict abortions and for the government to deny money to clinics that offer abortion advice or referrals. In the latest decision, Bush appointee David Souter provided the deciding vote, giving pro-choice forces ammunition to tie the president directly to the court's apparent willingness to weaken, and perhaps eventually overturn, the 1973 Roe vs. Wade decision legalizing abortion.

For Republicans, a bitter fight over abortion could threaten GOP gains among women and moderate, suburban voters in the 1980s; both groups tend to favor abortion rights and were swing voters in 1989 gubernatorial elections won by pro-choice Democrats. Or, if abortion-rights supporters gained the upper hand, the often-reluctant support Bush gets from the GOP's conservative wing could be undermined.

Yeutter's views notwithstanding, some party leaders believe some accommodation to pro-choice forces will have to be made in the 1992 GOP platform. The late Lee Atwater, Yeutter's predecessor, had hoped to mediate the dispute and avoid a convention confrontation that could scar Bush's celebration.

''Abortion is not as clear cut an issue as some of the purists on both sides would like it to be,'' said GOP activist Haley Barbour. ''I think the 1992 Republican platform will be pro-life but I don't think it will be addressed in black and white terms because in the wake of the court decisions you now have to deal with a host of middle-ground issues. We will have to accommodate the fact that circumstances have changed since 1988.''