The president of Mitsui O.S.K. Lines America Inc., says the Japanese carrier is shortening the transit time of its Far East-to-U.S. Pacific Southwest service and is initiating a direct call from Singapore to Los Angeles.

Minoru Nishioka, the line's top U.S. officer, said the carrier will begin the Singapore service May 23 to take advantage of the growing import market between Southeast Asia and Los Angeles. He cited manufactured electronic goods, footwear and textiles as imports the carrier will pursue.Singapore will be used as our hub in Southeast Asia, Mr. Nishioka said.

Tsutomu Iizuka, assistant vice president for Mitsui said the market is expanding to countries surrounding Singapore, such as Malaysia, Indonesia, Thailand and the Philippines. He said cargoes produced in those countries will be transshipped to Singapore for the U.S. market.

The 240-square-mile island nation of Singapore is home to 2.5 million people and has one of the world's busiest seaports.

Singapore's largest trading partner is the United States. In 1986, imports to and exports from the United States reached $2 billion and $1.2 billion, respectively. Singapore has become known as second only to Tokyo as a modern Asian city.

Mitsui will offer a 19-day transit time between Singapore and Los Angeles, a time the carrier claims is shorter than any other Japanese line in that

trans-Pacific service. However, Maersk Line, the Danish carrier, makes the Singapore-to-Los Angeles run in 17 days.

Six containerships will be committed to the Singapore trade, Mr. Nishioka said. He said three of those ships will be built in Japanese shipyards this year. The ships will be capable of holding 2,907 20-foot containers and achieving a service speed of 23 knots.

Mr. Nishioka said Mitsui can be competitive in the marketplace with these new ships since it plans to have them flagged in Panama. By doing so, the ships will be led by Japanese officers but can be crewed by Southeast Asian seamen, who command a lower salary than Japanese crews.

Mitsui also is making improvements in its Far East to U.S. Pacific Southwest trade route. Five ships are committed to this trade route and will reduce the turn around time of each ship by one week, Mr. Iizuka said.

The carrier's new transit time to Los Angeles will be reduced to 24 days

from Bangkok, 21 days from Manila, 15 days from Hong Kong, 14 days from Busan, 13 days from Kaohsiung, 11 days from Kobe and nine days from Tokyo.

Cargo volume in 1987 moving from the three major countries of Hong Kong, Taiwan and South Korea still accounted for as much as 80 percent of Mitsui's cargo total.