ONE RECENT MONDAY AFTERNOON, I was trying to tunnel myself out of the stacked papers on mydesk when I heard one of my colleagues in the next office explain how to pronounce my name to an incoming caller.

"Magnier" is indeed a strange name that is routinely massacred, so I knew I either had a caller I had never spoken with or someone with a bad memory. Think of Grand Marnier without the family fortune, I sometimes tell people. (There must be a lot of liqueur drinkers out there - that one seems to do the trick.)The call was switched through and the first words at the other end were: ''You hear so many bad things about the U.S. merchant marine. I was wondering if you might tell a good story about them."

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THE FIRST THING to cross my mind at that point was that I was now being called on to defend the honor and glory (or lack thereof) of the journalistic profession.

These occasional calls usually begin with a tirade about the unfair, wretched, inaccurate, obstinate, rude, mooching, always-get-it-wrong, back- stabbing, fact-fearing free press, followed by, "And while you're at it, why don't you guys ever print some good news?"

But this caller, who identified himself as Capt. R.L. "Jack" Frost, had something different on his mind. And after listening, I had to admit he did have a pretty good story.

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ON APRIL 26, Capt. Frost was going to work aboard the 125,000-deadweight- ton Arco Anchorage, which had sailed from Valdez, Alaska, and was bound for Martinez, Calif.

The captain, aged 69, has been a river pilot in San Francisco since 1951 and was scheduled to bring the oil tanker up the river from San Francisco Bay.

But things didn't quite work out that way. Jack had a minor mishap on the pilot ladder climbing onto the ship and found himself out of breath when he reached the deck. He took the elevator up to the bridge and was still winded so he asked to sit down, then he decided he'd better lay down. "Then I knew I was in trouble," he said. "I told them I couldn't take them up the river." His heart had stopped.

The crew of the Arco Anchorage had medical training, and its impromptu team kicked into gear. They brought oxygen, started CPR and got him "jump- started." Then they lashed him into a basket, suspended him over the side onto a waiting water taxi, shot him over to Pier 15 to a waiting ambulance and had him at the hospital within 30 minutes.

"By the good training these fellows have, they saved the life of a pilot," he said. "I should've been dead. Now I'm sitting here back at work again."

Capt. Frost said if he'd been a little further up the river it would have been too late.