nvironmentalists will start running a series of advertisements today to turn up the pressure on Gov. George E. Pataki to shut down the Indian Point nuclear power plant, which they call a terrorist target and a threat to millions of people.

The ads, financed by the group Riverkeeper, include an ominous television spot with satellite views of Indian Point at the center of an immense bull's-eye. The narrator speaks of the "evacuation zone" and "peak fatality zone," and says, "within the peak injury zone, there are some pretty big towns," as the camera zooms in to Manhattan.

Riverkeeper's campaign raises the volume and the political stakes of one of the most heated issues in the Hudson Valley. The television ad will appear in New York City and the Hudson Valley, and will coincide with print ads in Metro-North Railroad stations and some newspapers.

Officials at Riverkeeper say they hope to force the governor's hand now, because they believe he will be more likely to move against the plant under the pressure of a political campaign, when he has more to fear from public opinion, than after the election. Polls show Mr. Pataki with a sizable lead over his Democratic rival, H. Carl McCall, who has said the plant should be closed.

Mr. Pataki's office would not comment directly on the ads, or on the concerns raised by Indian Point's opponents. Instead, a spokesman read a statement that said Mr. Pataki had "launched the most comprehensive effort in the nation to combat terrorism and enhance safety at public facilities across the state."

In the past, the governor has declined to take a position on shutting down Indian Point.

Larry Gottlieb, spokesman for Entergy Nuclear Northeast, which bought the two operating Indian Point reactors in the last two years, called Riverkeeper's campaign "an act of desperation," and he accused the group, which has not made an endorsement in the gubernatorial race, of "using their dollars to push one candidate over another."

The movement to shut down Indian Point ballooned after the Sept. 11 attacks, when one of the airplanes that struck the World Trade Center flew down the Hudson, almost directly over the plant, raising questions about what would happen if it was hit.

Experts in nuclear power and federal officials have said that nuclear power plants could be terrorist targets.