Cement barriers, 8-foot-tall chain-link fencing, and heavy black netting have been installed around the protest zone outside the FleetCenter, angering protesters who say they will be penned in and closed off from Democratic National Convention delegates.

Much of the area is located under abandoned elevated Green Line tracks that slope downward. The setup, which one netting installer called ''an internment camp," will force tall protesters at the southern end of the zone to lower their heads to avoid banging them on green metal girders.

Furious that protesters are being shoehorned into an enclosed space, lawyers for the American Civil Liberties Union and the National Lawyers Guild said they will ask a federal judge to open up or move the zone.

''We were given every assurance that there would be an adequate space for people to assemble for purposes of protest that is within sight and sound of the convention and the delegates," said John Reinstein, an ACLU lawyer representing activists planning to protest at the convention. ``This is neither. . . . It's a pen."

Both the netting and a clear plastic sheet that the city plans to attach to the fences were designed to prevent protesters from hurling objects at delegates, many of whom will be arriving on buses near the protest zone, according to Mary Jo Harris, legal adviser to the Boston police.

The space is a 28,000-square-foot rectangle near Canal Street. Harris said the city did not alter the size or location of the protest area since talks with lawyers representing activists began months ago. ''But candidly, seeing it with the fence surrounding it has been a reality check for [protesters]," she said.

Still, she insisted that the protest area puts demonstrators closer to delegates than at any previous convention.

''What we have envisioned is a space where those demonstrators who want sight and sound access to the delegates can have that access, without jeopardizing the safety of the delegates or the demonstrators," she said. ''That is our intent, and that is what I expect."

The ACLU and the National Lawyers Guild are scheduled to appear in federal court at 11 a.m. today on behalf of a coalition of Boston activists, union members, and two Boston city councilors who were denied a permit to march on Causeway Street, in front of the FleetCenter, last Sunday afternoon.

Upon seeing the fences and netting around the protest area, representatives of both legal groups said they will challenge its location and design at today's hearing or file a separate lawsuit.

The creation of ''free speech zones," often far from the events that activists are picketing, has become a fierce controversy and the subject of lawsuits recently. When President Bush attended a meeting of world leaders last month on Sea Island, Ga., protesters were kept several miles away.

On Monday, a federal judge in Manhattan issued an order that blocked New York police from using pens made of interlocking metal barricades at demonstrations outside the Republican National Convention without ensuring that protesters can get in and out. The judge also said that police cannot close streets and sidewalks leading to protest sites without informing the public of other ways to get to the demonstrations.

In Boston, representatives of activists have been unhappy with the protest zone, across Causeway Street from the FleetCenter, for some time.

Urszula Masny-Latos, executive director of the Massachusetts chapter of the National Lawyers Guild, said she was upset when Harris informed her Friday that activists will be forbidden from setting up tables inside the confined area to distribute brochures.

Harris, the legal adviser to the police, said yesterday that tables are banned because they can be used as weapons.

But the fencing, Jersey barriers, and netting are what prompted civil libertarians to threaten lawsuits. The lawyers are representing at least three groups that have received permits to rally in the area: United for Justice with Peace, the Boston Coalition for Palestinian Rights, and the Bl(a)ck Tea Society.

The Bl(a)ck Tea Society, a self-described antiauthoritarian group, has issued a call on its website for members to boycott the ''free speech zone." The group says such zones violate free speech and can be dangerous because they confine groups often at odds with one another.

Shane Flood, one of the workers who installed the netting yesterday in the hazy sunshine, said the protest area was an insult to activists. ''I'd call it an internment camp," said Flood, 25, who works for Concert Staging Services, a Sutton company that also sets up stages for performances.

The city has issued about 100 permits to activists staging demonstrations and marches that begin this weekend. Police say it's hard to estimate how many protesters will turn out at any event, but they are using 10,000 as the uppermost figure. A police official who asked for anonymity said officers expect that 300 to 500 militant protesters may be willing to engage in violence.

- Steve Kurkjian of the Globe staff contributed to this report.