WASHINGTON — The Supreme Court appears likely to strike down a Massachusetts law setting a 35-foot protest-free zone outside abortion clinics, with liberal and conservative justices alike expressing misgivings today about the law in arguments.

The justices questioned the size of the zone and whether the state could find less restrictive ways of ensuring patient access and safety.

No one has been prosecuted under the 2007 law, which state officials and clinic employees have said has resulted in less congestion outside the clinics.

The court — which bars protests on its plaza, but allows them on the public sidewalks — last considered abortion clinic protest zones in 2000, when it upheld a Colorado law.

It seemed possible that there could be more than the five votes needed to strike down the law after Justice Elena Kagan said she was “hung up” over the size of the zone.

But it was hard to tell whether the court might also upend its 2000 ruling in support of the Colorado zone, which has been criticized by free speech advocates for unfairly restricting protesters’ rights.

That’s because Chief Justice John Roberts, normally an active questioner, did not ask a question of any of the three lawyers who argued the case.

Painted semicircles outside Planned Parenthood clinics in Boston, Springfield and Worcester mark the spot beyond which abortion opponents are free to protest and try to persuade women not to end their pregnancies. Inside the line, protesters and supporters alike risk arrest.