WASHINGTON (AP) _ Secretary of Defense Dick Cheney said today the landing of American troops in Somalia was going ''very well, very smoothly,'' and suggested that the withdrawal could begin by Inauguration Day.

''We're very pleased with the results'' of the first hours of Operation Restore Hope, during which U.S. Marines quickly and without resistance secured the airport and seaport of the Somali capital of Mogadishu, Cheney said in interviews with television networks and The Associated Press.

''All the reports we've been getting are that everything has gone very well, very smoothly,'' Cheney said this morning. ''There haven't been any problems.''

At a Pentagon briefing, Rear Admiral Michael W. Cramer said the security situation in Mogadishu was ''certainly satisfactory,'' with no signs of organized resistance as the first full day of the American presence neared an end.

Cramer, director of Current Intelligence in the Joint Chiefs of Staff, said there had been factional fighting in recent days in several towns where U.S. troops are headed later in the operation, but added that that, too, ''is beginning to resolve itself.''

Marine Corps Lt. Gen. Martin L. Brandtner said there were no plans to modify U.S. military deployment plans in the countryside as a result of factional violence.

At the White House, spokesman Marlin Fitzwater said President Bush called Gen. Colin Powell, chairman of the Joint Chiefs of Staff, this morning for a briefing.

According to Fitzwater, Powell told the president that everything was ''on track, on schedule and going as planned.''

''The president is obviously quite pleased by this opening phase,'' Fitzwater told reporters. ''He emphasizes that our purpose is to reduce the level of violence, and that appears to be happening at least up to this point.''

Fitzwater said Bush feels ''very highly about the conduct of our forces that have accomplished this mission so far with dispatch, as well as sensitivity to the civilian population. So far it's gone very well.''

Cheney said there was no chance of having all U.S. forces out of Somalia by the time Bush leaves office on Jan. 20. But he said the initial landings in the starving East African nation were a success.

''Based on the experience we've seen so far, I don't think it's unrealistic for us to expect once we get our people into the country, begin to get the U.N. peacekeepers going in ... that by the end of January we can have begun turning over authority to the peacekeepers.''

Cheney added: ''We will not be completely out by any means. I think that's completely unrealistic, but the notion that we could begin the drawdown of U.S. forces by Inauguration Day I think is not out of the realm of possibility.''

Cheney would not give a timetable for when U.S. troops will move out of Mogadishu into the countryside, but said the military was prepared to meet any resistance it might meet outside the capital.

''We have all of the resources we need to do the job.... I don't anticipate we're going to run into anything we can't cope with,'' he said.

The Marines in Mogadishu are turning their attention to getting the seaside airport ready for a long stream of Air Force cargo flights.

C-141s and other transport planes will ferry tons of supplies to Somalia for the U.S. forces there, and commercial airliners chartered by the military will start bringing in 16,000 Marines from Camp Pendleton, Calif.

Once the Marines declare the airfield secure for operations, the Air Force will immediately bring in people and equipment, such as runway lighting and forklifts for cargo unloading, to get the airport ready for round-the-clock operations, said Lt. Col. Randy Morger, a spokesman for the Tanker Airlift Control Center at Scott Air Force Base, Ill. The base is coordinating transport flights to Somalia.

An international ''air bridge'' of 24 KC-135 tanker aircraft to refuel the planes flying from the United States to Somalia is already in place, Morger said. A dozen KC-135s are at Lajes Field in the Azores and another dozen are at Moron Air Base, Spain, he said.

At a news conference in Washington before the Marines landed, President- elect Clinton indicated he saw no need to rush the Somalia mission to a conclusion.

''We believe that this mission has merit and that an artificial timetable cannot be imposed upon it,'' Clinton said. ''I respect and appreciate President Bush's desire to see the ground forces out of there by some time in mid-January, and it may work out that that can be done.''

Fitzwater said forces from several countries were being integrated into the overall operation, which was formally authorized last week by the U.N. Security Council as a last-gasp attempt to feed hundreds of thousands of starving Somalis.

The White House statement said Bush had spoken earlier Tuesday with Robert Oakley, the U.S. special envoy in Somalia. Oakley told the president that his discussions with relief agency representatives and Somali factional leaders were ''encouraging.''

Bush also spoke by phone Tuesday with U.N. Secretary-General Boutros- Boutros Ghali and discussed with him the latest developments and plans for the humanitarian mission.

Armed bandits and looters, many of them teen-agers, have paralyzed international relief agencies' efforts to feed the hundreds of thousands of starving Somalis. Tons of donated food are already in Somalia but cannot be distributed because of the threat of violence.