DENVER (UPS) — The head of the Federal Mediation and Consultation Ser vice is making a pitch to end the Oil, Chemical and Atomic Workers’ nationwide strike against refineries operated by about 100 oil companies. Wayne Horovitz and his assistant, Nik Finlandis, held a meeting late Wednesday with union officials and were scheduled to meet today with two industrial relations ex perts from Gulf Oil Corp. About 60,000 workers left their jobs Tues day in the first union-authorized strike against the industry in 11 years. Oil com panies have refused to meet demands for wage increases, more vacation time and fully paid health insurance. Horvitz said he would meet with union and industry officials separately until the opposing sides could sit down face-to-face and make progress. He was not willing to predict when direct negotiations might take place. Gulf Oil executives Merlin Breaux and Emory Kennedy arrived in Denver Wednesday to talk with the arbitrators, and Breaux indicated the union’s demand for fully paid health care benefits was the ma jor issue. “The company feels it is healthy to have employees participate in the medical plans with a monetary contribution,’’ Breaux About 60,000 workers left their jobs Tuesday in the first union-authorized strike against the oil industry in 11 years said, ‘‘But we’re keeping all avenues of communications open.” Breaux also said the Carter adminstra tion had been in touch with Gulf officials to emphasize the company’s obligation to negotiate a satisfactory agreement quick ly. “So far everything is friendly on both sides,’’ he said. ‘‘There is no animosity.” Oil companies across the country settled into the routine of having supervisors run their predominately automated refineries on the second day of the walkout, and there were only scattered incidents of violence or vandalism by strikers. Two refineries in Wyoming and Texas ceased operations because of the strike, an Oklahoma Refining Co. plant in Cyril was partially closed, and the strike also shut a Cities Service butyl rubber plant in Lake Charles, La., but total refinery production was reported near normal. In Colorado, headquarters of the 200,000-member union, only about 275 workers were on strike in Denver and Fruita. “There isn’t any way you can put a time limit to it (the strike),’’ said Bill Howard, refining marketing manager at Texaco’s facility in Casper, Wyo. ‘‘If we had to, (the refineries) could be operated this way forever.”’ Beds and kitchens were set up for super visory personnel at strikebound Amoco and Rock Island plants in Indianapolis. A striking picket was hit by a car and suf fered leg bruises at a Chevron Oil refinery in Richmond, Calif., Wednesday. Police said they were seeking the driver of the auto, which had been blocked from leaving the 365,000 barrel-a-day refinery by a picket line. A bullet fired by a high-powered rifle went through a window at an unoccupied of fice in the administration building of the Chevron refinery Tuesday, and at Avon, Calif., a security guard suffered cuts on the forehead when the pickup he was driving was hit by rocks allegedly thrown by a picket. In Kansas and Missouri, Teamsters Union drivers crossed picket lines to pick up refined petroleum products.