A United Steelworkers union bargaining committee yesterday agreed to an $18-an-hour labor contract offer from Wheeling-Pittsburgh Steel Corp. in what both sides said was the last chance to save the company from liquidation.

The local steelworkers' union presidents on the committee voted 13 to 6 to accept the company's offer. It must now be ratified by union members, who have been on strike since July 21. The agreement also would have to be approved by the bankruptcy judge handling Wheeling-Pittsburgh's Chapter 11 petition, which gives the company protection from creditors' suits while it tries to work out a new financing and operating plan.

Steel industry experts said that if the tentative agreement is put into effect, it may well create precedents for other steel companies that are also staggered by heavy debts and underfunded pension commitments. The agreement would give the steelworkers two seats on Wheeling-Pittsburgh's board of directors, only one of which would have voting rights.

The Wheeling-Pittsburgh offer would provide $17 an hour in wages and benefits, $1 for a new supplemental pension plan, and up to $1 more in bonuses tied to future increases in steel prices.

"This agreement represents the very best this negotiating committee could achieve, and the very best the company could offer," said Paul D. Rusen, chairman of the USW negotiating committee, and Andrew Palm, the committee secretary.

"Approval by the membership will mean we have saved our jobs, we have saved our town and, as we have promised, we have saved this company," the union leaders said. The balloting of union members will be done by mail and is expected to require up to two weeks.

But the company's future -- and the number of the company's 8,200 employes whose jobs are saved -- will depend as well upon the response of Wheeling-Pittsburgh's creditor banks, which are owed $322 million in debts remaining from an ambitious company expansion plan begun in the late 1970s.

The bank group, headed by Manufacturers Hanover, had backed a previous company plan that would have held labor costs to $16.55 an hour. The company's demands for wage and pay concessions of that magnitude, and the union's refusal to go along, precipitated the strike and a stalemate that each day took the company closer to liquidation.

Now, industry sources expect that the banks will seek a commitment from the company to close unprofitable installations.

The agreement includes a new, less-costly pension plan to take the place of the company's existing federally guaranteed plan, which is underfunded by $425 million.

Most, but not all, pension provisions under the earlier plan are protected by the federal Pension Benefit Guaranty Corp. The $1-an-hour supplemental pension contribution by the company in the new plan is meant to cover some of the lost benefits, union sources said.

The escalator clause giving steelworkers up to $1 an hour more and the addition of membership on Wheeling-Pittsburgh's board were praised as milestones by the union. "What this means is that we will be active participants in the reorganization of this company. We will have a major voice in how the reorganization takes place and what the new . . . firm will look like," Rusen and Palm said in a statement yesterday. "No other labor union has ever been able to do this."