'Giant' find off West Coast may ease US demand for foreign oil

Several weeks after major oil companies began to go public with news of what is billed as the biggest oil find since Alaska's North Slope, it is possible to begin assessing that find.

Chevron USA and Phillips Petroleum recently announced that test wells in the Santa Maria Basin, offshore some 60 miles north of Santa Barbara, indicate a field that will eventually produce 100 million to 300 million barrels of oil. Shortly thereafter, Texaco USA announced that its test well on a nearby tract also has produced evidence of a major field.

In oil industry parlance, a field with reserves of 100 million barrels is a ''giant,'' and the full extent of the discovery isn't yet clear. By comparison, the North Sea field, where oil was discovered in 1969, contains an estimated 14. 8 billion barrels of reserves. The North Slope has an estimated 8.7 billion. Some early estimates place potential reserves in China's offshore field, still being probed, at twice the size of the North Sea reservoir. Saudi Arabia's total estimated reserves comes to 164.6 billion.

Several known factors justify labeling the California giant ''friendly'':

* The oil is of good quality. Samples from two test wells indicate petroleum ranging from ''medium heavy'' (20 degrees specific gravity) to ''medium light'' (up to 34 degrees specific gravity), says Chevron spokesman John Hamilton. ''Light'' crude oil, above 35 degrees, is the least expensive to convert to gasoline and other commercial products. But the petroleum off Point Arguello apparently will be of immediate commercial value.

* Extraction will be relatively simple and inexpensive, and production should begin fairly soon. The depth at which the oil lies (around 8,000 feet) means it is well within the limits of present technology. General weather and water conditions in the area pose no special problems.

* Potential ecological impact appears slight, and resistance from many environmentalists unlikely. A spokesman for the Sierra Club points out that the field, about four miles off Point Arguello, is in an area where oil companies have been drilling for some time. The environmental impact of production should be acceptable, the club says, with normal safeguards.

Mari Gottdiener, offshore oil analyst for the California Coastal Commission, says the field is in a ''critical navigation area'' and that care will have to be taken not to interfere with the north-south shipping routes. She also says that the Coastal Commission probably will insist that a pipeline, not tankers, be used to bring the oil onshore.

Under federal law, the oil companies involved must present a plan that is consistent with Coastal Commission policies. In case of disagreement, the US secretary of commerce makes the final decision.

What will the new field mean for the American consumer and how will it affect US dependency on imports? That remains to be seen, says Stephen Chamberlain of the American Petroleum Institute in Washington, D.C.

He points out that US oil consumption is running about 7 million barrels a day. That means a field with a reserve of 300 million barrels contains some 43 days' supply. Also, notes Mr. Chamberlain, even a 1 billion-barrel reserve looks more like a midget than a giant alongside total American oil production, which was 2.97 billion barrels in 1980. (The 1981 figure, not yet available, will be less.)

But, according to Chamberlain and other industry specialists, the impact of a discovery like that off California can be significant, both in regional and global terms. If the Point Arguello field begins producing several thousand barrels a day for the California market in early 1986, as expected, this would free more Alaskan oil for purchase in other sections of the country. The additional California oil would also have some impact on the cost of oil imported by the US, these analysts point out.

There's a morale factor involved, too, say industry sources. Exploration in East Coast areas - Georges Bank off New England and Baltimore Canyon off the mid-Atlantic coast - has been unproductive. Expansion of fields in the Gulf of Mexico and onshore in the Gulf States continues, but that oil is getting more expensive. A bitter battle between the Reagan administration and environmental groups over drilling in park, wilderness, and other areas already is under way.

Discovery of a giant oil field not very far from Ronald Reagan's ranch has to give the President, and a lot of other Americans, a big boost, at least.