The Oil, Chemical and Atomic Workers union temporarily put aside its strike weapon yesterday and agreed to a 48-hour extension of contract talks with oil industry negotiators in Denver.

The union also softened its primary bargaining demand for a strict "no-layoff" agreement opposed by industry representatives, and it dropped its proposal that employers assume the full cost of employe health insurance premiums.

But the OCAW leaders defined what they meant by their earlier call for "a substantial wage increase." They're asking for a 13.5 percent raise in the first year of a two-year contract. That pay hike would be 3.9 percent higher than the average annual inflation rate of 9.6 percent for 1981.

Industry bargainers yesterday were offering an increase of 8 percent in the first year and 6 percent in the second year of a two-year agreement.

Some 400 separate contracts covering 55,000 OCAW oil refinery workers were scheduled to expire last night at midnight. Settlement traditionally comes first with large companies, such as Gulf Oil Corp., which set contract patterns for the rest of the industry.

Rank-and-file union members had voted to strike at midnight if no such agreement had been reached by the negotiators.

But the Federal Mediation and Conciliation Service, which had been monitoring the oil talks since they began early last November, asked both sides to continue talking for at least 48 hours. OCAW President Robert F. Goss agreed, saying that he was "deferring strike action at this time."

Gulf spokesman Kirk Vogeley, whose company is the largest involved in the talks, said his company accepts the extension and "looks forward to continuing negotiations to resolve the issues."

The union struck for three months in l980 in an effort to win wage and benefit improvements in a two-year contract, with a mid-term reopener clause, signed in 1979. OCAW came out of the dispute with 0.52 cents an hour more in straight pay and an extra $1 an hour for night shift work.

But the companies struck back by closing plants and laying off workers in areas deemed unprofitable. Goss said the closing of about 50 plants cost his union 5,000 members since 1980.

That's why the union wanted the strict "no-layoff" provision. But industry resistance forced the union to offer a "more flexible plan" for job security, OCAW spokesman Jerry Archuleta said last night. Under the union's new proposal, for example, a company using outside contractors for maintenance jobs would furlough those workers before laying off union workers. Normal attrition--retirements and resignations are examples--"would be allowed to function" in cases where a company has no outside contractors, Archuleta said.

Instead of full employer funding of health plans, the union now is asking the companies to kick in an additional $30 a month, Archuleta said.

Industry representatives reached last night said their companies had not yet responded to the union's new proposals.