By Mai Nguyen

VIENTIANE (Reuters) - Controversial Philippine leader Rodrigo Duterte donned a lounge suit for his first international summit on Wednesday, a rare show of sartorial conformity as pressure mounts on him to act presidential.

The maverick former city mayor, who was shunned on Tuesday by the White House for insulting U.S. President Barack Obama over his bloody "war on drugs", looked dapper as he posed for pictures in a classic, two-button charcoal suit and silk tie.

Filipinos are drawn to Duterte's no-nonsense, man-of-the-people style, which sits oddly with the pomp and protocol he encountered at this week's meeting of Southeast Asian leaders in Laos.

He typically wears a polo shirt, jeans and slip-on loafers and on formal occasions has dressed in a barong, a traditional long-sleeved Filipino shirt, which he wore at a gala dinner on Tuesday.

Salvador Panelo, the presidential legal adviser, said Duterte found suits uncomfortable but he probably wore one to try to blend in better in the international political arena.

"The problem is wearing a barong, when people are wearing black suits, you stand out," he said.

"Maybe he might feel embarrassed as the center of attention. Did you see, he was a rock star? He wants to be less conspicuous ... Our president is a very good and humble fellow."

Duterte, 71, once said he had never owned a suit and does not wear socks.

In his first month in office, he ordered sharp spending cuts on red-carpet state events and issued a decree outlawing use of the term "Excellency" for himself and ministers. His aides say he prefers to be called mayor rather than president.

White House officials were dismayed on Monday when Duterte - responding to criticism over the killing of hundreds of suspected drug dealers since he came to office - used the term "son of a bitch" during a news conference in which he lashed out at Obama.

The White House then called off a meeting with Obama that was scheduled for the following day in Laos.

Duterte subsequently issued a statement expressing regret that Obama was offended.

Japan Prime Minister Shinzo Abe met the Philippine leader on Tuesday and told Duterte he was "very excited" to meet him in person because he had become famous among Japanese people.

(Reporting by Mai Nguyen; Writing by Martin Petty)