West Coast longshoremen went back to work peacefully Tuesday after refusing to service most containerships up and down the coast Monday.

The massive "sick-out" - a term the International Longshoremen's and Warehousemen's Union doesn't use - was a protest over the loss of some 335 jobs at an intermodal railyard in Los Angeles.Although longshoremen Monday shut down almost all port activity in Los Angeles/Long Beach, the nation's busiest container complex, the dockworkers were not as successful in northern California and the Pacific Northwest.

The Pacific Maritime Association, the San Francisco-based group that represents maritime employers on the West Coast, confirmed that a Sea-Land Service Inc. containership was worked in Tacoma, Wash. Also, an automobile carrier operated by Maersk Inc. was worked in the northern California port of Benicia and a number of bulk and breakbulk vessels were worked in the Pacific Northwest.

Longshoremen in Oregon and Washington state showed the least inclination to support union members in Southern California.

''Basically, the Northwest worked," said Ray Holbrook, regional vice president in San Francisco for Stevedoring Services of America, a Seattle- based stevedoring company with operations at most West Coast ports.

Mr. Holbrook added: "In northern California, those of us who ordered workers got them."

Nevertheless, about a dozen containerships sat idle at various Pacific ports Monday, either because their operators declined to request work gangs or were unable to get them. Some shipping lines submitted orders for work crews but got none, said Terry Lane, vice president of the Pacific Maritime Association.

In Los Angeles and Long Beach, for instance, a total of seven containerships had been scheduled to unload Monday, but none were worked that day.

All of the vessels that were idled Monday were being worked Tuesday, sources said.

According to ILWU spokesman Danny Beagle in San Francisco, what happened Monday was a show of support for longshoremen who lost their jobs when the Southern Pacific Transportation Co. turned over work at the Intermodal Container Transfer Facility in Los Angeles to a rival rail union.

He said the union received "tremendous support" from longshoremen in the Pacific Northwest who attended the rally in Los Angeles.

The ILWU now faces a court date next Monday. It is under an order from a U.S. District Court in Los Angeles not to disrupt activities at West Coast ports or the ICTF. The ILWU must show cause to Judge Robert Takasugi why his temporary restraining order should not be made permanent. Mr. Beagle said the union had no comment on that order.

Judge Takasugi issued his order in response to formal charges filed last week by the National Labor Relations Board. The NLRB, after gathering evidence

from the Pacific Maritime Association, determined any stop-work activity by the union would be a secondary boycott action against maritime employers.

The NLRB determined that the union's complaint is with SP, not maritime employers.

James McDermott, regional attorney for the NLRB in Los Angeles, said the ILWU may be able to avoid the court date Monday by signing a "stipulation to refrain" from unfair labor practices. However, the union could also choose to argue its case before the court.

Mr. McDermott indicated the Pacific Maritime Association could sue for damages if it is determined that the refusal by longshoremen to work Monday was an organized job action. Shipowners incur losses of more than $50,000 each day a modern container vessel sits idle.

Terry Lane, maritime association vice president in San Francisco, said the employers' group is consulting with its attorneys and no decision has been made on what further legal steps, if any, will be taken.

Mr. Lane confirmed that longshoremen up and down the coast were back on their jobs Tuesday.

"It's a busy day today," he said.