Just after learning that President Bush planned to nominate federal appellate judge John G. Roberts Jr. for the Supreme Court, NARAL Pro-Choice America sent an electronic action alert yesterday to its 800,000-person network, encouraging members to call their senators and talk to friends about their opposition.

The abortion rights group also sent out 30,000 e-mails to its activists around the country last night, outlining talking points explaining its opposition to Roberts, and furnishing sample letters to be sent to local newspapers and background on the nominee. The group planned to follow up today with calls to its 27 national affiliates, keeping them abreast of any new information about Roberts, who was appointed to the U.S. Court of Appeals for the District of Columbia in 2003.

Conservative interest groups, meanwhile, voiced strong support for Roberts and began their campaign for the nominee long before he was announced. Hours before Bush spoke, Progress for America staff members were working in the 20th Street studios at Interface Media, preparing a biographical ad supporting the nomination that will be ready to air on cable television within 48 hours.

"We understand the crucial importance of defining the nominee before the opposition has a chance to," said Jessica Boulanger, the group's director of communications, who said it is prepared to spend $18 million or more. "The amount we spend will be dictated by how much the left puts into fighting the nominee."

Organizations on both sides have spent years preparing for this moment. Their legal experts have been poring over the records of potential nominees, and organizers have spent many hours in planning meetings and on conference calls to hone their messages. Also, they have amassed huge war chests to finance television, radio and print ads to define the nominee in the public's mind.

The stakes are high because with the retirement of Justice Sandra Day O'Connor, who has been a crucial swing vote on the court, many liberal activists fear -- and conservatives hope -- that Roberts would move the court decidedly to the right.

But in the frenzied aftermath of Bush's selection of Roberts, it was unclear whether his nomination would produce the battle royale that was widely anticipated. Liberal activist Jesse L. Jackson, NARAL and some other groups immediately opposed Roberts, whom they view as hostile to abortion rights, but many other liberal groups looked at his relatively spare judicial record -- he ascended to the appeals court bench in 2003 -- and were left as many questions as answers.

"His views and judicial philosophy are clearly well known to the president who nominated him, and the Senate owes a duty to the American public to be sure that it knows and that the public know what his view are," said Marcia D. Greenberger, co-president of the National Women's Law Center.

Officials at People for the American Way held conference calls with allies throughout the day, as speculation swirled about Bush's choice. After the announcement, the liberal activist group activated a plan to mobilize its 750,000 members. "We're extremely disappointed that the president did not choose a consensus nominee in the mold of Sandra Day O'Connor," said Ralph G. Neas, president of the group. Although Neas stopped short of immediately opposing Roberts, he said the nominee raises "serious questions."

The group zipped e-mails to 400,000 members urging them to contact their senators, asking them to closely scrutinize the nominee.

Although many liberal groups attempted to portray Roberts as a nominee with a limited judicial record that nonetheless raised troubling issues, many conservative groups said he fits their definition of a jurist who would strictly interpret the Constitution.

Jan LaRue, chief counsel to Concerned Women for America, said the conservative group is preparing a grass-roots campaign to support Roberts if Democrats threaten to filibuster. "Everything I know tells me he meets the president's criteria very well; he clearly is in the mold of [Antonin] Scalia and [Clarence] Thomas" -- both conservative justices.