Any chance of a floor fight on a controversial issue at next week's Republican National Convention was apparently eliminated today when conservative forces simply rolled over delegates favoring the Equal Rights Amendment and free choice for women on abortion.

As the full Republican platform committee began its final markup of the 1980 platform, its 106 members chose not even to vote directly on the ERA and abortion issues.

Instead, they substituted langauage acknowledging "the legitimate efforts of those who support or oppose the Equal Rights Amendment" in place of a proposal to restore the Republicans' traditional support for ERA. That substitution carried 90 to 9, and there was no further effort to get another vote on the proposed constitutional amendment, which previous Republican platforms since 1940 have endorsed consistently.

Then the platform committee voted 75 to 18 to table, thus to kill, a proposal to tone down an abortion plank that favors a constitutional amendment banning all abortions.

The outcome on both issues satisfied Ronald Reagan's aides here. The Reagan forces were prepared to accept planks on both issues that leaned somewhat further toward a fuzzy middle-of-the-road position, but as it stands the platform will reflect the positions Reagan has long taken.

That will cost the Republicans votes in November, warned several members of the platform committee, including Massachusetts Rep. Margaret M. Heckler, who spoke passionately in favor of the ERA.

Heckler warned her colleagues that their attempt to "compromise" on the ERA by neither supporting nor explicitly condemning it would not wash with the American women who have made the amendment a symbol of their struggle for women's rights. "In their eyes there is no way" to support equal rights without also backing the Equal Rights Amendment, she told the committee, but it ignored her.

Heckler and other pro-ERA Republicans here said they would accept today's vote, however, and not try to press the issue on the floor. In all likelihood, they lacked the 27 signatures from platform committee members that would have been needed to bring the ERA before the entire convention.

Representatives of the National organization for Women (NOW) passed out leaflets, just before this afternoon's platform committee session, announcing plans for a rally Monday to lobby the convention to endorse ERA again. The rally may go on, but its objective will be out of reach.

Similarly, there appeared to be no chance that the abortion issue would be carried to the floor of the convention. And in this conservative Republican year, when the overwhelming number of Republican delegates seem comfortable at the Reagan end of the political spectrum or still further to the right, these appeared to be the only genuinely controversial issues before the platform committee.

Today delegates proposed amendments to the platform such as changing the word "Democratic" to "Democrat" wherever it appears in the document, or adding a plank acknowledging the inviolable status of the automobile as America's principal means of transportation.

The committee also adopted a declaration of support for the aspirations of black Americans, promising that Republican economic policies would help them as much as whites.

Generally, the delegates were able to march smartly through the platform draft before them, approving whole sections without any proposed changes. The smoothness of this process is indicative of the overwhelming strength that one faction will hold in this convention. In all likelihood, the full convention will do its business without a single serious argument among Republicans appearing on television.

The platform committee is somewhat more conservative than the convention as a whole, because it is organized like the U.S. Senate, with two votes for each state plus six extra for the District of Columbia and American possessions. Thus the Republican parties in big industrial states which tend to be relatively moderate are substantially underrepresented on the platform committee.

Washington-area delegates played visible roles in today's proceedings. Guy O. Farley of Warrenton, Va., proposed the substitute motion that buried the pro-ERA forces. Jan A. K. Evans of Washington proposed eliminating all language on abortion from the platform on the grounds that "this is a personal issue" inappropriate to a political document. Her idea was rejected by a voice vote.