Is petroleum a renewable resource?

Discovery that petroleum is being formed today in a hot-water vent in the Gulf of California has changed Peter Lonsdale's perspective on oil.

''This may mean that petroleum can be a renewable resource under proper conditions of heat and pressure and that our Earth does not have a finite amount that can be exhausted,'' says the Scripps Institution of Oceanography geologist.

It is a long leap from discovering that petroleum, or petroleum-like substances, form rapidly in hydrothermal vents to concluding that oil may be a significantly renewable resource. However, as Lonsdale and many other oceanographers constantly point out, these hot-water vents are an important marine environment that was scarcely suspected to exist a decade ago. Its role in the ocean has only begun to be understood.

The vents flow from cracks where the sea bed is splitting apart to form a new ocean floor from lavas welling up from below. Circulating through the hot underlying material, the waters flowing from the vents are rich in minerals. They also support rich communities of animal life at depths of thousands of meters, where such life had not been expected. Among other creatures, a 25 -centimeter fish of a previously unknown species has recently been found in such a community.

Every expedition to one of the vent areas produces surprises. The joint Canadian, Mexican, and United States expedition to the Guaymas Basin, with Lonsdale as chief scientist, made two major discoveries. It found extensive mats of yellow-white-orange bacteria described by microbiologists as the ''largest (bacteria) they have ever seen.'' And it found ''young'' petroleum that forms in only thousands of years, as opposed to millions of years for fossil oil.

Describing the findings in a press release issued by Scripps and in a report to Nature coauthored with Bernd R.T. Simoneit of the University of California at Los Angeles, Lonsdale describes how the hot, mineral-rich waters of the vent, at a depth of some 2,000 meters, transform organic matter mobilized from seabed sediments into oil. This is probably done at temperatures greater than 250 degrees C., as opposed to a maximum of 150 degrees C. for normal petroleum-forming processes.

Consequently, the so-called ''young'' petroleum has a somewhat different mix of organic chemicals from that of ordinary oil, although it includes molecules in the gasoline range.

Extensive deposits of zinc, copper, and iron sulfides were also found. Lonsdale says these ''should not be of commercial interest.'' However, such sulfide deposits elsewhere have created enough interest in the mining industry for the US Congress to consider amending the Deep Sea Mining Act to take account of them. The value of a single deposit, located off Oregon, is put at $3 billion.

Thus hydrothermal vents are becoming an important factor in ocean mineral wealth. Will they also one day be important for oil? It is much too early to judge. But, at the very least, the vents provide a natural laboratory to study the chemistry of oil formation.