Protest was strongest in the capital, where police arrested more than 300 members of the anti-abortion movement after they blockaded three abortion clinics, at one site chaining themselves to cars which had been wedged in clinic doorways.
Bill Clinton has issued decrees overturning five pieces of Bush-Reagan legislation. He rescinded a law banning federally financed clinics from offering abortion counselling, opened the door again to US funding for international family-planning programmes and lifted a ban on medical research using foetal tissues.
The ending of the ban on counselling, dubbed by pro-choice activists as the 'gag rule', was welcomed by the Planned Parenthood Federation, which runs 900 clinics across the country. The law, championed by George Bush, had been blocked by a federal judge but was due to come into force next month. Dozens of clinics had been threatened with closure.
'Overturning the gag rules literally saves the ability of low-income American women to have family planning and deal with unwanted pregnancies,' said David Andrews, the acting president of the federation. 'Otherwise we would have had a public-health disaster on our hands.'
Mr Clinton's order is also welcome news for international agencies, including the United Nations, engaged in family planning projects in Africa and other Third World regions. The US was a leading force in population-control efforts until the mid-1980s, when President Reagan withdrew funding from all programmes that included some abortion element.
'What we're seeing is the United States returning to the fold, and that's very important,' said Sharon Camp, the vice-president of Population Action International, a Washington-based group.
Officials at the UN Population Fund voiced hope that US funding for their programmes would be quickly resumed. Until the Reagan order, the fund received dollars 46m (pounds 30m) a year.
The new attitude of the Clinton administration is certain to provoke sustained protest from the 'right-to-life' activists, however. At the weekend protest, a spokesman for 'Operation Rescue', the leading anti-abortion group, warned that the President was 'forcing us . . . to bring the battle on to the streets'.
Hundreds of hymn-singing Operation Rescue members blockaded three Washington clinics on Saturday morning in an effort to turn away prospective abortion patients. They were met by equal numbers of pro-choice advocates, who responded by chanting abortion-rights slogans. In one incident, police took two hours to disentangle protesters from cars used in the barricades.
The Vatican made its own views known through the columns of the L'Osservatore Romano, the newspaper often used to convey papal policy.
Under President Clinton, the US had 'embarked on the paths of death and violence against innocent beings', it said.