Indiana became the 35th state yesterday to ratify the Equal Rights Amendment - with more than a little help from a Rosalynn Carter phone call.

The state Senate caucused in Indianapolis and was deadlocked at 25 to 25 yesterday morning. Sen. Birch Bayh (D-Ind.), sponsor of the ERA, called President-elect Jimmy Carter in Plains, Ga., to urge him to lobby for the measure. Carter wasn't around, so Rosalynn Carter took over, according to Bayh aide.

She called Democratic state Sen. Wayne Townsend, known to be wavering in the caucus, and persuaded him to switch his vote. Then the Indiana Senate, which had killed the ERA twice before and spent several days of heated debate on it this time, approved it by a vote of 26 to 24. State legislator Townsend was unavailable for comment on Rosalynn Carter's lobbying ability.

The ERA - which would prohibit discrimination because of sex - requires ratification by three more states by March 22, 1979, to become the 27th Amendment to the Constitution.

Legislators in North Carolina, Nevada, Florida and the President-elect's home state of Georgia will take up the ERA measure in the next two months.

Betty Ford, the outgoing First Lady, set a precedent for Rosalynn Carter's phone calls in behalf of the amendment to Arizona legislators in 1973, but the measure was defeated 16 to 14. The First Lady drew criticism from anti-ERA forces for using her White House clout to promote ratification.

In Indiana, pro- and anti-ERA forces had campaigned stronger than ever before. State senators were deluged by hundreds of telephone calls and letters for or against. Yesterday the Senate gallery and hallaways were packed with spectators and a roar went up in the gallery after the vote was tallied.

The Indiana ratification broke a logjam: it has been two years since North Dakota became the 34th state to ratify the amendment.

Women's rights group hailed the Indiana vote as a "needed breakthrough." "Indiana's passage of ERA so early in the year is a clear indication that ratification of the amendment is closed at hand," said League of Women Voters President Ruth Cluson. "We are confident that those states which have been gearing up for passage of the amendment will now follow suit and pass ERA this year."

Not all people were happy, especially those demonstrators who waved signs in the state Capitol yesterday that said, "ERA is Not the Way." Said a chief Indiana ERA foe, Republican State Sen. Joan Gubbins: "I'm very much in favor of equality of opportunity but not a doctrinaire, absolute equality."

Legislatures in two states - Nebraska and Tennessee - have voted to rescind their ratification, but the legality of that move has not yet been determined.

Pro-ERA leaders across the county concede that the amendment probably will die unless it is ratified by at least two of the three remaining states this year.

ERA proponents are concentrating on five states - North Carolina, Nevada, Missouri, Oklahoma and Florida - as among the most likely to ratify the amendment in 1977.

Supporters of the ERA in Virginia are hoping to force a vote later this week on a procedural change that would bring the amendment to the floor of the 100-member House of Delegates for the first time. It has been bottled up in a hostile House committee, but ERA supporters are hoping to win approval of a new rule that would require a House vote on all constitutional amendments.

Efforts to force reconsideration of the issue in the Virginia state Senate may be understaken later in the session by a committee which last year killed the amendment by a one-vote margin.

Liz Carpenter, co-chairperson of ERAmerica - a national coalition of more than 120 pro-ERA organizations said, "Being against equal rights is the same type of bigotry as being against civil rights. It is never easy to overcome bigotry but 35 states have done it. Indiana has seen the light and we know this will show the way to lost souls in the state legislatures who have not acted."