OTTAWA (AP) _ Air Canada and its ground workers reached a tentative contract settlement Wednesday to end a strike that had grounded the national carrier since Nov. 27.

Workers across the country began returning to their jobs a few hours after federal mediator Bill Kelly announced the deal. Air Canada spokesman Pierre Jerome said the airline would be in full operation by Friday, when the Christmas rush and school holidays begin.

The settlement is subject to ratification by Air Canada's 8,500 mechanics, baggage handlers, ramp attendants, cargo agents and cleaners, all members of the International Association of Machinists and Aerospace Workers.

Ron Fontaine, the union's chief negotiator, said the ratification process would start next week. He predicted the settlement would be ratified in about two weeks.

Air Canada normally carries up to 40,000 passengers daily during the Christmas rush. Officials said the airline would continue offering refunds to ticket holders booked up to Jan. 3 and would cut fares by as much as 60 per cent on some runs during the holiday travel period.

Montreal ticket agent Jean Caron said Wednesday's sales were 80 percent lower than normal for this time of year. Some industry analysts said Air Canada may never regain the 48 percent market share it had before the strike.

''We're just going to have to start over from scratch and fight like hell just to get back to where we were before,'' said Jerome. ''It's like we have to start up all over again.''

He said the airline lost several million dollars during the strike. Union spokesman Bob Biggar estimated that the airline lost $47.5 million Canadian ($36.5 million U.S.).

Pierre Jeanniot, Air Canada's president, shut the airline last month after a series of rotating strikes by the union. Negotiations broke down twice over the union's demand that members' pensions be protected against inflation.

Fontaine, the union negotiator, said Air Canada gave in on the major issue of indexing pensions to the inflation rate. In return, the airline got the union to agree to a three-year contract with annual wage increases of 4 percent for each of the first two years and 5 percent for the last year.

The union had sought a 12 percent increase in a two-year contract.