The General Motors Corp. and the Ford Motor Co. yesterday offered the United Auto Workers a new wage and benefit package that UAW President Douglas A. Fraser described as "a foundation upon which we can build . . . a satisfactory agreement."

As expected, the union rejected the industry's first contract offer in more than six weeks of bargaining, and Fraser characterized some of its provisions as "troublesome."

But Fraser's caution and muted comments, coupled with concern over the auto industry's vulnerability to a recession, appeared to lessen the once-heavy odds of a strike when the UAW'S three-year contracts with the Big Three automakers expire Sept. 14.

The GM and Ford offers, reportedly almost identical although the two companies bargain separately with the union, came only two days before the UAW is to choose one of them as its target for concentrated final-stretch bargaining and possibly a strike.

The UAW earlier ruled out the financially troubled Chrysler Corp. as a strike target.

GM, despite its size and financial strength, has been considered the most likely target for this year, although some observers believe that Ford, the 1976 target, still could be chosen. Earlier this week, the UAW called off a series of threatened "mini-strikes" against GM after reportedly making satisfactory progress on local issues, including noninterference with union organizing at southern plants.

Neither GM nor Ford disclosed details of the new three-year offers, but, like most other major contracts negotiated this year, they appeared to exceed the Carter administration's guideline of 7 percent a year for wage and benefit increases.

According to bargaining sources, the two companies offered to continue their recent pattern of 3 percent annual wage increases, along with their current cost-of-living formula that recovers about 80 percent of wages lost to inflation, now running at an annual rate of about 13 percent.

The UAW is seeking a formula that would give workers 100 percent protection against inflation, and, as its main new bargaining goal, also is demanding a cost-of-living adjustment for pensions.

GM and Ford proposed no cost-of-living changes but reportedly offered some pension improvements.

In a tacit acknowledgement of the UAW'S drive for a shortened work-week the companies offered 19 paid "Personal" days off over the three-year life of the contract, an increase of seven days over the current contract. The UAW is seeking more than that.

Ford and GM reportedly made no mention of the union's proposal for compensatory time off in addition to overtime pay as an incentive to spread available work among more workers. The companies also reportedly proposed several potentially explosive "takeaways."

These included more stringent controls on absenteeism, which the companies regard as a serious and mounting problem, and a lower starting wage for new hires.

For instance, to curb absenteeism, they would require a worker who takes a Monday as a "personal" holiday to work the preceeding Friday as well as the following Tuesday. The worker now is required only to work Tuesday.

The starting-pay differential would be increased from 45 cents to $1.10 an hour, and it would take longer -- a year instead of 90 days -- to get full wages and benefits.

Big Three auto workers currently get about $9 an hour in wages and $5 to $6 in benefits. GM, for instance, calculates its total average hourly labor cost at $15.10.

GM characterized its offer as embodying "substantial increases in wages, pensions and additional paid time off the job . . . which recognizes the needs of our employes and addresses the major concerns expressed by the union." Ford described its proposal as "responsive to the legitimate needs of our hourly employes and consistent with the realities of an environment in which we are operating."