Another showdown in the long struggle between tradition and change in the American labor movement is shaping up at the center of the nation's energy industry.

The recent history of militant challenges to union orthodoxy has generally been long on fanfare and lean on results, bigger in the mass media than among rank-and-file union members.

But the current battle for leadership of the 180,000-member Oil. Chemical and Atomic Workers Union (OCAW) appears to be different.

In the first place, it has gotten almost no attention outside the oil refineries and chemical plants that have been organized by the Denver-based union. Also, both contenders are top officers with strong followings within the union, and the outcome is not a foregone conclusion.

Moreover, although the union's hold over the oil industry is sharply curtailed by extensive automation, the importance of the industry gives the union potential prominence that transcends its numbers and bargaining leverage. And the results could ripple through the entire labor movement in a time of impending leadership changes reaching all the way up to George Meany, the ailing 84-year-old president of the AFL-CIO.

By conventional standards, Robert Goss, a popular union vice president with years of broad experience in the OCAW, should be a shoo-in to succeed Al Grospiron, who is retiring after 14 years as president.

But he has encountered strong opposition from Anthony Mazzocchi, a more recently elected vice president who, as the union's longtime Washington representative, became one of the labor movement's leading advocates of occupational health and safety protections.

In a campaign that goes far beyond health and safety issues, Mazzocchi has attacked Goss as a "business-as-usual" candidate with "his feet planted firmly in yesterday" and with "no vision or strategy for the future." Says Mazzocchi: "The union movement has become bureaucratized, and Goss is the epitome of it."

In response, Goss seeks to make a virtue of being, as he call it, an "internal nuts-and-bolts union man...with broad experience in the day-to-day operations of the union."

In a thinly veiled reference to Mazzocchi, Goss has criticized "emotional rhetoric" and tried to portray the choice as one of a doer vs. a talker. "My main thrust," he said in an interview, "is that you have to have someone who is proven and trusted. If you have a problem, you sit down and work it out."

"Instead of sitting at our desks," responds Mazzocchi, "we should be out at the gas pump telling people what's really going on...out talking to workers who are saying, "Where the hell have you been?" Among other things, he has called for more labor involvement in progressive coalition movements and a "global" union strategy for dealing with multination corporations like the oil companies. As for "emotional rhetoric," he says, "I think it's time for a little emotion to creep back into the labor movement."

Assuming that Grospiron's successor would take the union's seat on the AFL-CIO Executive Council, a Mazzocchi victory could be expected to churn the normally tranquil waters of the council's quarterly gatherings. The kind of institutional soul-searching that Mazzocchi advocates is not a customary agenda item.

Whether a Mazzocchi victory would stimulate ferment in other unions is unclear, although some observers contend that any addition to the thin ranks of union militants is bound to be felt.

Goss and Mazzocchi are campaigning intensively for support of delegates being chosen for the OCAW convention Aug. 17 in Florida. The convention will elect the new president, and sources within the union say the race now is too close to call. CAPTION: Picture 1, ANTHONY MAZZOCCHI; Picture 2, ROBERT GOSS...both contenders are top officers with strong followings within the Oil, Chemical and Atomic Workers Union