WASHINGTON — Wary of alienating Jewish voters, the campaign of Senator Obama has moved swiftly to remove an ad for its Web site that appeared on the Amazon.com page of a book critical of the Israel lobby.

A small ad for barackobama.com was one of a group of advertisements that rotated as “sponsored links” on the page for “The Israel Lobby and U.S. Foreign Policy,” a book by John Mearsheimer and Stephen Walt that has drawn rebuke from supporters of the Jewish state. The Illinois senator’s campaign said it had bought ads on Amazon.com to appear with the keyword category of “politics” through a subsidiary of the popular Internet shopping site.

The placement on the “Israel Lobby” page was unintentional, a campaign spokeswoman said, and the ad was gone hours after a New York Sun reporter notified the campaign of its location. “The ad has been removed from the site because the views of the book do not reflect the views of Senator Obama on the U.S.-Israel relationship,” the spokeswoman, Jennifer Psaki, said.

In the book, Mr. Mearsheimer, a professor at the University of Chicago, and Mr. Walt, a professor at Harvard University’s John F. Kennedy School of Government, argue that a powerful “Israel lobby,” which they say includes politicians, journalists, scholars, and students, has steered the government into supporting Israel in ways that run counter to American national interests.

Ms. Psaki said that although Mr. Obama had not read the book, he was familiar with its arguments and disagreed with them. “Senator Obama has stated that his support for a strong U.S.-Israel relationship, which includes both a commitment to Israel’s security and to helping Israel achieve peace with its neighbors, comes from his belief that it’s the right policy for the United States,” she said. “The idea that supporters of Israel have somehow distorted U.S. foreign policy, or that they are responsible for the debacle in Iraq, is just wrong.”

Like many of his Democratic rivals, Mr. Obama has courted Jewish voters, and he has won praise from pro-Israel groups. In April, he told the National Jewish Democratic Council that his commitment to Israel was “unwavering.” The Amazon incident is the second time in a month that the Obama campaign has publicly acknowledged removing an inadvertently placed Internet ad, and it underscores the uncharted territory that campaigns are navigating as they look to lure potential voters to their expansive Web sites. In August, the Obama campaign removed an ad purchased through Google that appeared on a site dedicated to derailing his top rival, Senator Clinton, according to a report in the New York Observer’s Politicker Web log.

Campaigns purchase Internet ad space that is keyed to search words. In this case, the Obama campaign said it had used the “politics” category in its Amazon buy, so that viewers who searched for books about politics might see the Obama ad as a “sponsored link.” Ms. Psaki would not say whether other keywords were involved, and a spokesman for Amazon, Andrew Herdener, would not comment on specific accounts.

Mr. Herdener said links on a specific page can be removed upon request and that clients also can specify “negative keywords” if they want to prevent their ad from appearing on certain pages.