Conservative forces on the Republican platform committee today easily pushed the Grand Old Party off its traditional support of the Equal Rights Amendment, then put the GOP squarely behind a constitutional amendment to ban all abortions.

Abandoning the position the party has adopted consistently since 1941, a platform subcommittee voted 11 to 4 to endorse the concept of equality for women but not to back the ERA itself. The approved plank condemns Carter administration efforts to pressure states to ratify the amendment.

Pro-ERA activists here promised to press their case in the full platform committee, and on the floor of the national convention next week, but they appear to have no chance of renewing Republican support for the amendment.

The subcommittee on human resources ignored arguments that it was flouting majority opinion in the country and thus narrowing the GOP's appeal in November by taking the conservative line on both ERA and abortion. Delegates seemed much more interested in registering their strong feelings on both issues.

Interest in ERA and abortion was greater than in any other issue before the platform committee. The room in mammoth Cobo Hall where the human resources subcommittee met was filled with reporters, cameras and spectators, most of them women wearing red anti-ERA or green pro-ERA buttons. Other subcommittees considering issues like energy, fiscal policy, defense and foreign policy and agriculture did their drafting work without any spectators to speak of.

On abortion, the position adopted seems to conflict clearly with the views of the great majority of convention delegates. According to Washington Post poll of a random sample of 602 delegates, 65 percent oppose a constitutional amendment outlawing abortion and 28 percent approve one. However, by a 42-to-28 margin, with 30 percent expressing uncertainty, the delegates polled said they felt that Reagan favored such an amendment.

There were essentially three different positions on both ERA and abortion in the human resources subcommittee. One element -- clearly the dominant one -- favored strong positions against a constitutional amendment on equal rights and for one that would ban abortions. A small feminist faction favored strong positions on the opposite side of both those issues. And a third group, which did succeed in moderating the instincts of the hard-line element, sought to write fuzzier platform planks that would be easier for Ronald Reagan to run for president on in the fall.

In effect, proponents of the most conservative line agreed to let the planks be a little fuzzy provided the pro-ERA and pro-abortion forces did not get their way.

"Anything that is detrimental to our [that is, Reagan's] election in November is so frightening," said panel member Betty Rendel of Peru, Ind., that the committee must moderate extreme views to attract more voters. She pleaded specifically for adoption in the platform of a "bill of rights" for American women, which was indeed approved after the decision was made to withdraw GOP support from the ERA.

But stronger sentiments were obvious. Donald E. White of Anchorage, Alaska, for example, argued in debate that supporters of ERA were "naive or devious" if they didn't acknowledge that adoption of the amendment would mean eventual adoption of "unisex facilities" in aspects of American life. "Radical supporters of ERA" are actually promoting "the eradication of the American family," he declared. White later identified himself as director of the Alaska branch of the Moral Majority, a fundamentalist New Right group which White said had five members on Alaska's 18-member delegation to the national convention.

The motion to put the GOP clearly behind a constitutional amendment banning abortion was made by Guy O. Farley Jr. of Warrenton, Va. When votes were taken, Farley said he was casting his "for hundreds of thousands of unborn children."

Though the results on these two issues were lopsided, they represented the closest thing to a real fight on an important matter among all the platform committee's deliberations here today.

The Republicans are proceeding in a manner dramatically different than did the Democrats a fortnight ago in Washington, when serious struggles between pro-Carter and pro-Kennedy factions were common.

Here, the delegates are sticking closely to a draft platform prepared by the Republican National Committee in close consultation with the Reagan campaign. The document echoes Reagan's positions.

It calls for immediate tax cuts and tens of billions more for defense, while promising to "balance the budget without tax increases" by cutting spending in other, generally unspecified areas.

On energy, the draft platform argues for immediate, complete price decontrol plus aggressive use of coal and nuclear power and exploitation of renewable energy sources. It says the OPEC oil cartel is not to blame for American inflation, but the Carter administration is.

On one point, the draft GOP platform sounds just like the Democratic platform of 1976.

"The Democrats are now trying to stop inflation with a recession, a bankrupt policy which is throwing millions of Americans out of work."

Four years ago the Democrats made that accusation against the Republican administration then in power.