US president Joe Biden has blasted a “radical” draft Supreme Court opinion that would throw out the landmark 1973 Roe v Wade abortion rights ruling that has stood for half-a-century and warned that other rights, including same-sex marriage and birth control, were at risk if the court followed through.

The court confirmed the authenticity of the leaked draft, which was dated to February, and Chief Justice John Roberts said he had ordered an investigation into what he called an “egregious breach of trust”. A court statement emphasised that the draft was not the justices’ final word.

Opinions often change in the drafting process, and a final ruling had not been expected until the end of the court’s term in late June or early July.

A decision to overrule Roe would lead to abortion bans in roughly half the states, spark new efforts in Democratic-leaning states to protect access to abortion, and potentially reshape the contours of this year’s hotly contested midterm elections.

The draft was published by the news outlet Politico late on Monday.

Speaking to reporters before boarding Air Force One, Mr Biden said he hoped the draft would not be finalised by justices, contending it reflected a “fundamental shift in American jurisprudence” that threatened “other basic rights” like access to birth control and marriage.

He added: “If this decision holds, it’s really quite a radical decision.”

He said the “basic fairness and the stability of our law demand” that the court does not overturn Roe.

“If the court does overturn Roe, it will fall on our nation’s elected officials at all levels of government to protect a woman’s right to choose,” Mr Biden said.

“And it will fall on voters to elect pro-choice officials this November. At the federal level, we will need more pro-choice senators and a pro-choice majority in the house to adopt legislation that codifies Roe, which I will work to pass and sign into law.”

Although past efforts have failed, Senate Majority Leader Chuck Schumer said he intended to hold a vote.

“This is as urgent and real as it gets,” Mr Schumer said on the Senate floor on Tuesday.

“Every American is going to see on which side every senator stands.”

Whatever the outcome, the Politico report represents an extremely rare breach of the court’s secretive deliberation process, and on a case of such importance.

“Roe was egregiously wrong from the start,” the draft opinion states. It was signed by Justice Samuel Alito, a member of the court’s six-three conservative majority who was appointed by former president George W Bush.

The document was labelled a “1st Draft” of the “Opinion of the Court” in a case challenging Mississippi’s ban on abortion after 15 weeks, a case known as Dobbs v Jackson Women’s Health Organisation.

The draft opinion in effect states there is no constitutional right to abortion services and would allow individual states to more heavily regulate or actually ban the procedure.

“We hold that Roe and Casey must be overruled,” it states, referencing the 1992 case Planned Parenthood v Casey that affirmed Roe’s finding of a constitutional right to abortion services but allowed states to place some constraints on the practice.

“It is time to heed the constitution and return the issue of abortion to the people’s elected representatives.”

The draft opinion strongly suggests that when the justices met in private shortly after arguments in the case on December 1, at least five voted to overrule Roe and Casey, and Justice Alito was assigned the task of writing the court’s majority opinion.

Votes and opinions in a case are not final until a decision is announced or, in a change brought about by the coronavirus pandemic, posted on the court’s website.

The report comes amid a legislative push to restrict abortion in several Republican-led states — Oklahoma being the most recent — even before the court issues its decision.

Critics of these measures have said low-income women will disproportionately bear the burden of the new restrictions.

The leak jumpstarted the intense political reverberations that the high court’s ultimate decision was expected to have in the midterm election year.

Already, politicians on both sides of the aisle were seizing on the report to fundraise and energise their supporters on either side of the issue.

An AP-NORC poll in December found that Democrats increasingly see protecting abortion rights as a high priority for the government.

Other polling shows relatively few Americans want to see Roe overturned.

People on both sides of the issue quickly gathered outside the Supreme Court waving signs and chanting, following the release of the Politico report.

Reaction was swift from elected officials in Congress and across the country.

In a joint statement from Congress’ top two Democrats, House Speaker Nancy Pelosi and Mr Schumer said: “If the report is accurate, the Supreme Court is poised to inflict the greatest restriction of rights in the past 50 years — not just on women but on all Americans.”

Mississippi Attorney General Lynn Fitch said in a statement: “We will let the Supreme Court speak for itself and wait for the court’s official opinion.” But local officials were praising the draft.

“This puts the decision making back into the hands of the states, which is where it should have always been,” Mississippi state representative Becky Currie said.

Until now, the court has allowed states to regulate but not ban abortion before the point of viability, at around 24 weeks.