Nippon Yusen Kaisha Ltd., Japan's largest steamship line, is mulling a relocation of its Pacific Northwest terminal from Seattle to Tacoma, Wash.

NYK is based at the Port of Seattle but has discussed the possibility of moving to the Port of Tacoma or another Northwest port. It expects to make a decision by the first quarter of next year, an executive with the line said.Dodd W. Fiori, senior vice president of NYK Line (North America) Inc., said Tokyo-based executives for the Japanese steamship line have spent the past two years considering how to get the best facilities at the lowest cost.

"Cost is the main consideration," he said. "I can tell you without tipping our hand that every option in the Pacific Northwest doesn't cost the same."

Mr. Fiori said that even if a decision to relocate is made, it could be a year or two before NYK left Seattle.

"Any (new) port would need at least a couple of years to build us a new container terminal," he said.

He said that port charges alone are not the only factor that enter into NYK's evaluation of cost. Terminal facilities, labor productivity, rail access, local market share and transit times all affect cost, he said.

"We're talking to Seattle, but we've also talked to some other people about a terminal," he said.

"We are aware that NYK is in the decision-making process," said Cathy Keck, spokeswoman for the Port of Seattle. "We want to continue to serve them. We have such a long-term relationship with them - our 100th anniversary would be in 1996 - that we want them to take all the time it takes to make the right decision."

Jiro Nemoto, NYK's president, earlier this year said a recession and an erosion of trans-Pacific rates by non-conference carriers would limit NYK's earnings growth in 1993, but he expects a new surge of cargo growth in 1994 and 1995 to result in higher volumes and improved profits during those years.

John Terpstra, director of the Port of Tacoma, said the Tacoma port regularly advises steamship lines of the property it has available, but has not yet struck a deal with NYK.

The Tacoma port is doing preliminary work on a 50-acre container terminal but has not said which steamship line is likely to use it.

NYK is one of the larger trans-Pacific container lines calling at the Port of Seattle. Seattle has expanded its NYK terminal to 40 acres under a lease that runs through January of 1995.

Last month, Frank Clark, then marine director for the Seattle port, cited a new NYK service established in connection with NYK's strategic alliance with Neptune Orient Line as a reason for a jump in Seattle's container figures.

Seattle port commissioners a few weeks earlier had said they would expect either to have to provide direct rail yard access to terminals used by NYK and Hanjin Container Line or eventually to move their operations to Harbor Island.