Faced with mounting problems on Capitol Hill, White House officials clung yesterday to an optimistic view of the progress some of their key legislative proposals are making in Congress.

Presidential press secretary Jody Powell, answering a barrage of questions about congressional weakening of President Carter's energy plan, was moved near the end of his regular briefing to issue a personal challenge to reporters.

"If you want to put money on it," Powell said, "I would be willing to bet that we will win more than we lose."

Powell was responding to questions about the House Ways and Means Committee's decision to eliminate rebates for purchase of fuel efficient cars and to weaken a provision of the energy proposal that would impose a tax on large "gas guzzler" automobiles. That was before Carter suffered two other setbacks yesterday, defeat in committees of his proposed gasoline tax and his natural gas price plan.

The press secretary also paid the administration has not given up hope of passing legislation this year that would establish a consumer protection agency. White House strategists had hoped to pass the bill first in the Senate and then tackle the more difficult task of getting the measure through the House.

But on Wednesday, Senate Majority Leader Robert C. Byrd (D-W.Va.) said the Senate would not even consider the consumer protection agency legislation until it is approved by the House.

"We'll just have to get down in the trenches more in the House," Powell said.

Earlier yesterday, the Democratic congressional leadership met Carter at the White House and told him that there is not enough time this year to accomplish all his goals and that he should give them a list of his legislative priorities.

The President, according to House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), responded by suggesting that Congress move soon on reforming the Social Security financing system. Carter has proposed using income tax revenues to pay some of the cost of Social Security benefits and increasing the Social Security payroll tax on employers more than on employees.

O'Neill quoted the President as saying there is "grave concern" among the elderly, fed by stories in "the right-wing press," that the Social Security system is about to collapse.

The Speaker said Carter promised to develop a more detailed priority list and to have it delivered to the leadership in a few days by Vice President Mondale.

O'Neill said the leadership's own priority list "very definitely has the minimum wage on it," adding that he urged the President to seek a compromise on the issue with the AFL-CLO. Organized labor is seeking a minimum wage of $3 an hour, while Carter has proposed raising it from $2.30 an hour to $2.50.

O'Neill also said Carter praised the harmony between the administration and Congress and suggested that news reports to the contrary are misleading.