WASHINGTON — Expedia on Thursday won approval from antitrust officials to acquire rival Orbitz, a $1.3 billion deal that some consumer advocates and hotel associations feared would lead to higher prices for consumers and make it harder for small hotels to survive.

The Justice Department said its six-month investigation had found no evidence that the merger would reduce options for consumers. It noted that Orbitz is a relatively small source of bookings for airlines, car rental companies and hotels.

“We concluded that Expedia’s acquisition of Orbitz is not likely to substantially lessen competition or harm U.S. consumers,” Bill Baer, head of the Justice Department’s Antitrust Division, said in a statement.

“Many independent hotel operators, for example, do not contract with Orbitz, and those hotels that do often obtain very few bookings from its site,” he said.

The merger comes amid a tumultuous time for travel sites, which once dominated the search for and booking of hotels, airline flights and rental cars. Increasingly, these companies compete with search engines and hotels and airlines that have become more aggressive in reaching out directly to consumers and cutting out online brokers.

Yet the tie-up combines the second- and third-largest online travel agencies in the country. And the American Hotel and Lodging Association has argued that the merger would create a “duopoly” between Expedia and Priceline, which will now control 95 percent of the online travel-marketplace, a business that generates $152 billion a year.

Perhaps unbeknownst to many, the majority of the most popular online booking sites are actually controlled by the two companies. Priceline owns Booking.com, OpenTable and Kayak. Expedia owns Hotwire, Hotels.com and Travelocity.