Joe Biden has warned that a leaked draft supreme court ruling overturning Roe v Wade, the 1973 case which guaranteed the right to abortion, would represent a huge change in America law and could imperil a wide range of other civil rights.

In a historic moment that shook the US to the core and highlighted jagged social and political divisions, the court confirmed the draft was authentic but said it did not “represent a decision by the court or the final position of any member on the issues in the case”.

Biden said the ruling, if handed down, would represent a “fundamental shift in American jurisprudence” and could imperil rights including same-sex marriage and access to contraception.

Politico published the draft by justice Samuel Alito on Monday night. The website said the draft was supported by four other rightwingers on a panel conservatives control 6-3.

On Tuesday the chief justice, John Roberts, called its leak a “betrayal of the confidences of the court” which could “undermine the integrity of our operations” and promised an investigation.

Speaking to reporters, Biden said the draft ruling had ramifications for “all the decisions you make in your private life, who you marry, whether or not you decide to conceive a child, whether or not you can have an abortion and a range of other decisions [including] how you raise your child”.

The draft ruling would allow states to declare abortion illegal.

Biden asked: “Does this mean that in Florida they can decide to pass a law saying that same-sex marriage is not permissible, [that] it’s against the law in Florida? It’s a fundamental shift in American jurisprudence.”

Protesters gathered outside the court and planned demonstrations around the country – both in support of and against abortion rights.

At the court, some chanted “Abortion is healthcare” and carried signs reading “Justices get out of my vagina”, “Legal abortion once and for all” and “We won’t go back”. A smaller group chanted “Hey, hey, ho, ho, Roe v Wade has got to go”. Amid tense exchanges, barriers were erected.

In a statement, Biden outlined how Democrats might fight back.

First, the president said, his administration would argue Roe was based on precedent and “‘the 14th amendment’s concept of personal liberty’… against government interference with intensely personal decisions”.

“I believe that a woman’s right to choose is fundamental,” Biden said. “Roe has been the law of the land for almost 50 years, and basic fairness and the stability of our law demand that it not be overturned.”

Biden said he had directed advisers to prepare responses “to the continued attack on abortion and reproductive rights, under a variety of possible outcomes”.

“We will be ready when any ruling is issued,” he said.

Politico said it received a copy of the draft, which also dealt with Planned Parenthood v Casey, a 1992 case, from a person familiar with proceedings in Dobbs v Jackson Women’s Health Organization, a Mississippi case due to be decided this summer.

The draft ran to 98 pages including a 31-page appendix of state abortion laws and included 118 footnotes.

Alito wrote: “Roe was egregiously wrong from the start. Its reasoning was exceptionally weak, and the decision has had damaging consequences. And far from bringing about a national settlement of the abortion issue, Roe and Casey have enflamed debate and deepened division.”

He added: “We hold that Roe and Casey must be overruled. It is time to heed the constitution and return the issue of abortion to the people’s elected representatives.”

As many as 26 states are expected to enact partial or total abortion bans if Roe falls. Some Republican-run states are expected to attempt to make traveling for an abortion illegal. Democratic-run states have indicated moves to protect and help women who seek an abortion.

Polling shows clear majority support for abortion access. Christian and conservative groups campaign to end it regardless.

If the court overturns Roe, Biden said, “it will fall on our nation’s elected officials at all levels of government to protect a woman’s right to choose. And it will fall on voters to elect pro-choice officials this November.”

Biden promised to sign legislation codifying Roe into law. On Tuesday, the Democratic Senate leader, Chuck Schumer, said: “This is as urgent and real as it gets. We will vote to protect a woman’s right to choose and every American is going to see which side every senator stands.”

But legislative success would require reform to the filibuster, a Senate rule which requires 60 votes for most legislation. Moderate Democrats have blocked such moves on issues including voting rights. Biden himself has expressed opposition.

Carl Tobias, a law professor at the University of Richmond in Virginia, told the Guardian: “This might not be the final ruling. The justices usually confer after arguments and suggest how they would resolve a case and then the senior justices in the majority and minority work on drafts and circulate them to all members of the court.”

He said: “In some cases, especially high-profile and controversial ones … justices do change their positions, as Chief Justice Roberts allegedly did” in a 2012 case in which the Affordable Care Act, popularly known as Obamacare, was upheld.

Laurence Tribe, a Harvard law professor, pointed to possible wider implications.

“If the Alito opinion savaging Roe and Casey ends up being the opinion of the court,” Tribe wrote, “it will unravel many basic rights beyond abortion and will go further than returning the issue to the states: it will enable a [Republican] Congress to enact a nationwide ban on abortion and contraception.”

Other rights that may be at risk if Roe falls include the right to same-sex marriage, determined in Obergefell v Hodges in 2015.

Charles Kaiser, a historian of gay life in the US and a Guardian contributor, said Alito’s opinion “blithely disregards past precedents”.

“One passage in particular sets off alarm bells for activists who think its reasoning could jeopardize the court’s decisions legalising sodomy and the right of members of the same sex to marry.”

In a sharply divided Washington, the supreme court is subject to fierce partisan warfare – particularly since Mitch McConnell, the Republican leader in the Senate, ripped up precedent to deny Barack Obama a third pick in 2016.

Republicans confirmed three justices under Donald Trump, including Amy Coney Barrett, a hardline Catholic conservative, just weeks before the 2020 election – a move which ignored McConnell’s own posturing four years before.

Biden has overseen the confirmation of Ketanji Brown Jackson, the first Black female justice, but she has not yet replaced the retiring Stephen Breyer, another liberal, in a move that will not change the ideological imbalance.

In the aftermath of the Politico story, Democrats pointed to the wider threat posed by the court.

Adam Schiff, a California congressman and chair of the House intelligence committee, told the Guardian: “In abandoning decades of precedent, the draft opinion exposes the supreme court as no longer conservative, but now merely a partisan institution bent on imposing its anti-choice views on the rest of the country.

“This decision, if made final, will be devastating for the healthcare of millions of women, even as it is destroys any semblance of devotion by the court to the law.”

Alexandria Ocasio-Cortez, the New York progressive, said: “[The court] isn’t just coming for abortion – they’re coming for the right to privacy Roe rests on, which includes gay marriage and civil rights.”

Republicans welcomed the draft ruling and condemned the leak – which the top legal reporter Nina Totenberg called a “bomb at the court”.

Josh Hawley, a hardline Missouri senator, called Alito’s draft “tightly argued, and morally powerful” and said of the leak: “The justices mustn’t give in to this attempt to corrupt the process. Stay strong.”

Among Republican moderates, Susan Collins of Maine – who under Trump supported the appointments of Neil Gorsuch and Brett Kavanaugh but voted against Barrett – pointed to a possible betrayal.

“If this leaked draft opinion is the final decision,” she said, “it would be completely inconsistent with what Justice Gorsuch and Justice Kavanaugh said in their hearings and in our meetings in my office.”

Among women’s rights campaigners, condemnation of the Alito draft was strong.

Laphonza Butler, president of the advocacy group Emily’s List, said: “It’s past time to vote out every official who stands against the pro-choice majority.”