The Delta-Northwest merger hasn't been approved yet, but officials of Atlanta's Hartsfield-Jackson International Airport are beginning to behave as if it's a done deal.

Officials of the city-run airport Wednesday got initial approval to expand one of Hartsfield-Jackson's five runways in anticipation of more international flights once the merger is approved.

The runway expansion means Hartsfield-Jackson would be able to handle more 400-passenger Boeing 747s, specifically 747-400s, which is the workhorse of Northwest Airlines' international fleet.

"We expect more large aircraft to be moved here from Detroit [after the merger]," airport deputy general manager Mario Diaz said in an interview after the city Transportation Committee gave its nod to spend $3 million for the design phase of the runway expansion.

Atlanta-based Delta Air Lines and Minnesota-based Northwest have agreed to merge the two carriers and form the world's largest airline, which would be called Delta and headquartered in Atlanta. Federal regulators and shareholders still have to approve the merger, which could close by year's end.

Detroit is a major hub for Northwest and is a jump-off point for many of its international flights originating in the United States.

Delta officials said Wednesday they have not made any decisions about transferring international routes from Detroit to Atlanta. Any route change would need regulators' approval.

Delta requested the runway expansion, officials said, to better accommodate its Boeing 777s, the airline's long-haul jet of choice. Delta is flying more of the big jets as it increases its international business.

International flights make up about 40 percent of Delta's business, a figure that could jump to 50 percent after the merger.

"We have not made any specific commitments or announcement regarding any additional international service out of the Atlanta airport related to the merger," said Delta spokeswoman Susan Elliott. She said the airline wanted runway 9L 27R lengthened to accommodate Delta flights headed to distant locations.

"This request has been in place for some time, and it's specifically related to the 777s," she said, noting that Delta would like the runway project completed by 2009.

Elliott said the runway expansion would give Delta the ability "to right-size aircraft to accommodate demand" on select routes out of Hartsfield-Jackson, the world's busiest airport. "This could mean additional long haul aircraft flying in and out of Atlanta," she said.

Elliott said the airline currently needs additional cargo capabilities on its 777s, and the new runway would help meet those needs. Delta's 777 tally is 10 now, and the airline will have 16 in its fleet within two years, she said.

"Long term, it could also present opportunities related to equipment we may acquire in the future," Elliott said.

The runway, the first of three southern runways from the terminal, is about 11,890 feet. The airport wants to add 500 feet to its eastern end and possibly another 900 feet on the western side. Diaz said he did not have a cost for the runway project.

Big jets can now take off from Hartsfield-Jackson with a full load of fuel, cargo and passengers during most weather conditions, Diaz told the Transportation Committee. But in extremely hot weather, they have to shed fuel or cargo. That means the airline loses revenue on cargo or the aircraft has to stop to refuel on a long trip.

The lengthened runway, he said, would permit the long-haul jets to take off during any weather conditions with full loads.

Diaz said the airport was specifically concerned about Boeing 747s, the long-haul aircraft used by Northwest.

The airline, according to its Web site, has 30 of the aircraft — 16 of the 400-passenger 747-400s and 14 of the freight-hauler 747-200s.