A supertanker carried a volatile cargo of reporters Wednesday through a narrow Alaskan fjord and deposited them safely on the dock at Valdez, the southern terminus for the trans-Alaskan oil pipeline.

The supertanker, which carried no oil, was the first to try the passage, which will have to be made thousands of times to get Prudhoe Bay crude from Valdez to market once the pipeline starts flowing this summer.

As Alaskan pilot William Tingley took the helm of the ARCO Fairbanks from Capt. Thomas DeTemple, the ship's master, and entered the deep channel, a hush fell upon the bridge, marred only by the whirring of television cameras and the soft chatter of the reporters who crowded the goldbraid ropes on either side of the wheel.

Drifting gray clouds hit the snowy peaks on either side of the Valdez Narrows. Three helicopters loaded with photographers hovered alongside the tanker like seagulls following a trawler. Two sea lions swam up beside the vessel, in flagrant violation of the Coast Guard safety zone.

And the ARCO Fairbanks glided into the calm waters of Port Valdez.

This trip was for the media, marking the halfway point in a month-long program designed to test the Coast Guard's Vessel Traffic Service in Prince William Sound and to train ships' masters and pilots under local conditions. The Vessel Traffic Service is an $8 million monitoring system similar to those set up in Puget Sound, San Francisco, and Houston since passage of the Ports Waterways Safety Act in 1972. Valdez's VTS establishes inbound and outbound lanes which tankers and other large vessels must follow through Prince William Sound. Tankers in the northern portion of the sound will be kept under radar surveillance, and the Coast Guard will keep in radio contac with all vessels in the system.

Friday, practice will resume in anticipation of June 20, when oil is scheduled to begin flowing south from Prudhoe Bay. It could take between 30 and 45 days to reach Valdez. (Noone knows for sure how long the trip south takes by pipeline, and betting pools are forming all over the state.

The tankers will start out slowly, making one trip a day, then two, and at peak production of a daily 1.2 million barrels, three tankers a day will make the round trip through the narrows. At 120,000 deadweight tons the ARCO Fairbanks is about average size for the Alaska fleet.

Month-long trials using the ARCO Fairbanks began April 6, when the supertanker reached Prince William Sound, having been taken off its regular run to the Persian Gulf. Until this week, the tests have been staged in the relatively open waters of Prince William Sound outside Valdez Arm. From now on the 883-foot-long vessel will be moving in the out of Valdez through the narrows.

Valdez Arm, and particularly the narrows, has been the object of most of the concern shown over tanker operations in the Sound. A loaded tanker coming out of Valdez will have to follow a path whose width pinches to 900 yards between a sheer mountainside on the left and a slightly protruding pinnacle known as Middle Rock on the right.

In a recent series of computer-simulated runs through the narrows sponsored by the state of Alaska and held in the Netherlands, Dutch pilots piled up their "tankers" on the rocks with unnerving frequency. Many of the runs were staged with conditions that were extreme even for the south central Alaska coast - the land of the occasional 40-knot-plus "Valdez Wind." A number of the stimulated accidents also resulted from surprise equipment failures that were occasionally programmed into the runs.

Industry officials say the narrows are still wider - if windier - than the entrance to some other world supertanker ports.Coast Guard officials, who are responsible for overseeing the safety of the operation, like to point out that one could jam 18 Alaska-trade tankers side-by-side into the 900-yard space.

The cost of the trials has been estimated by ARCO at over $2 million. Wednesday on board the ARCO Fairbanks, the consensus of operating personnel was that the trials are helping fine-tune the Coast Guard's Vessel Traffic Service and providing useful practice for local pilots and more than 40 tanker captains.

No one expected the supertanker to get a scratch on its first trip into Valdez.

"I think the navigational problem here has been overblown," said Capt. W. E.Murphy, one of the three Alaskan pilots on the bridge of the ARCO Fairbanks during its first trip through the narrows.

"The first run will be a space shot," predicted Frank Tupper, an organizer of a Concerned Coastal Citizens group. "What we're worried about is the human error that can take place months after the line is in operation, when everything's become routine."