President Bush on Monday pledged continued troop support for South Korea and called for lower trade barriers as he wrapped up a five-day Asian trip and headed home to a fierce political battle over John Tower's nomination to head the Pentagon.

"I have come here today as the leader of a faithful friend and a dependable ally," Bush said in a speech to the South Korean National Assembly that highlighted his quick stopover in Seoul. The president boarded Air Force One at 5:24 p.m. local time (3:24 a.m. EST) for the nearly 15-hour return trip to Washington. He made a brief stop in Alaska for refueling just before noon EST.The president's audience applauded when he pledged to keep the 42,000 U.S. troops on duty as protection against North Korea, but sat quietly when he talked of trade.

"I want you to have this direct from me: if we are to keep our bilateral relationships growing even stronger, much more needs to be done" to ease trading relations, said the president.

Although Bush's South Korean visit was limited to five hours, a security force of 120,000 police, agents and commandos was put on top alert to protect him against threats ranging from radical students to North Korean infiltrators.

About 700 radical students shouting "Bush go home!" battled riot police with firebombs and rocks during a 45-minute clash around Dongguk University in an abortive attempt to march on the U.S. Embassy about three miles away.

Earlier, police arrested about 15 prominent dissidents shouting "no Bush visit" who had tried to assemble about a block from the embassy in downtown Seoul.

Minutes after they were hauled away, Bush's helicopter flew overhead on its way to the Blue House, the nearby presidential mansion, after his arrival from China at a secure military base outside Seoul. Police also clashed with demonstrators in five other cities, including the site of a U.S. air base south of Seoul.

From Seoul, Bush was flying back to Washington and the sternest political test so far of his young administration, the storm over the Tower nomination. The appointment is in danger of rejection in the Democratic-controlled Senate, and the president has pledged to mount a personal lobbying campaign to salvage it.

Bush's brief visit in Seoul included a luncheon for which the participants took off shoes and donned slippers. Guests sat on a heated floor on cushions with hard backs. But the 6-foot-2 Bush had trouble stretching his legs, asking his hosts, "Do you put your legs straight out or do you fold them up?"

The president made his rounds of Seoul by helicopter as he met with President Roh Tae-woo - a democratically elected leader who replaced the country's unpopular military dictatorship - addressed the South Korean National Assembly and greeted U.S. Embassy employees.

In the Blue House meeting, Bush and Roh held a 15-minute meeting that included discussions on the trade issue. "Korea has benefitted from the United State's open market," Bush said in remarks to reporters after the session.

Roh said he had briefed Bush on "all our efforts for the reduction of tension and consolidation of peace on the Korean peninsula," including what he called "a forward-looking policy toward North Korea."

Dissident calls statement a start

BEIJING (AP)

Fang Lizhi, the dissident whom Chinese police prevented from attending a banquet given by President Bush, said Monday the president's statement of regret was "a beginning" but he hoped for more.

White House press secretary Marlin Fitzwater said Bush learned Monday that Fang and his wife were barred from the banquet Sunday night and that the president "expressed regret" to Vice Premier Wu Xueqian before flying to Seoul, South Korea.

Fitzwater said it is the president's view that such problems as human rights should be dealt with in a low-key and private manner.

The 53-year-old Fang, China's most famous dissident, is also an internationally respected astrophysicist.