WASHINGTON — Google’s rivals have again prompted antitrust investigators at the Federal Trade Commission to examine the company’s business practices, and staff members have begun a preliminary look at whether Google abuses its market dominance in online display advertising, like the banner ads on Web pages.

People who have been contacted in connection with the inquiry said that the F.T.C. had begun asking questions about Google’s practices, specifically whether the company was bundling advertising services together in a way that prohibited rivals from competing for the business of advertisers.

The F.T.C. said in December 2007 that it would monitor Google’s practices in that area. At that time, the commission found that Google’s proposed acquisition of DoubleClick, an online advertising company that specialized in display ads, was “unlikely to substantially lessen competition.”

“We want to be clear, however,” the F.T.C. wrote at the time, “that we will continue to watch these markets and, should Google engage in unlawful tying or other anticompetitive conduct, the commission intends to act quickly.”