President Carter, turning his attention from the Cabinet shakeup to energy proposals, found Congress newly skeptical yesterday.

In a last-ditch attempt to spur action on his "windfall profits" tax, Carter summoned members of the Senate Finance Committee to a late afternoon meeting at the White House but failed to dampen the panel's sentiment for weakening the bill.

Moreover, Carter's proposals for an $88 billion synthetic fuels program and an energy mobilization board to ride herd on new projects encountered initial criticism at several congressional hearings.

The one bright note for Carter came when the House Rules Committee cleared the way for a vote today on a new version of the president's standby gasoline rationing plan. The House rejected the first version in May, 246 to 159.

The new skepticism in Congress marked the lawmakers' first serious reaction to Carter's proposals since the president's televised speech July 15. Congressional attention last week was diverted to his Cabinet shakeup.

The questioning was interpreted in part as a sign that Carter's energy effort lost some momentum during the week of Cabinet firings, which appeared to disturb many key congressment.

Carter's concern about the windfall profits tax involved plans by key Finance Committee members to dilute the proposed tax bite in the name of spurring increased production.

The president was reported to have told the Finance Committee members that if the panel weakened the windfalll bill, the government would not be able to finance the programs needed to meet its 1990 energy goals.

The White House estimated earlier that enacting two of the committee's expected amendments -- exempting's newly discovered oil and small independent producers -- would slash the measure's tax take by $55 billion over 10 years.

Sources said the president's plea appeared to have little impact. The committee is expected to consider not only those amendments but provisions to exempt Alaskan and stripperwell oil as well.

Committee Chairman Russell B. Long (D.La.) also told Carter that, contrary to White House hopes, the panel would not complete action on the "windfall profits" bill before Congress' August recess.

Long indicated instead that the two houses most likely would send the bill to Carter's desk by Oct. 1 but did not promise what would be in it. Carter had wanted the earlier date to sustain momentum begun in the House.

The Finance Committee voted yesterday to use all the proceeds from the "windfall" legislation for either general tax reductions or energy-spurring "incentives," even if it adopts the House bill intact.

The administration missed a second deadline yesterday for sending the lawmakers its own proposal on how to distribute the portion of the "windfall profits" tax money that is earmarked for aid to the poor. Although the White House made no formal statement on the matter, sources said key Carter planners are unable to agree. The administration asked the lawmakers for another week to mull ths issue.

In yesterday's sparring: Carter's proposals for a massive new synthetic fuels program came under criticism and questioning at two Senate committees, with panel members expressing serious reservations about both the details and the risks. Three congressional committees began considering sharply differing versions of Carter's proposed "fast-track" procedures to speed development of synthetic fuels, raising the prospect of delays and bickering later on.

Sen. Henry M. Jackson (D-Wash.) told reporters Carter probably would win passage of the basic elements of his July 15 energy plan, but would have to settle for minor but significant changes.

The Rules Committee vote clearing the way for House floor action on the standby gasoline rationing plan was regarded as a welcome development by the administration. The bill is expected to pass both houses this time.

The skepticism about Carter's synthetic fuels plan came in separate hearings of the Senate Energy and Government Affairs committees. Members were critical particularly of what they said was White House failure to provide more details.

Energy chairman Jackson said he will support Carter's proposal for an energy security mobilization board, but does not want financing of the synthetic fuels program tied to the windfall profits tax, which he predicted would be too weak.

In discussing the reasons for postponing action on the tax, Long said the Finance Committee partly was concerned about the plan for distributing the monies and wanted to wait until it passed the House.

The administration had proposed the broad outlines of a plan when it unveiled the windfall profits tax, but postponed sending up details at the request of House leaders, who feared it might mire the bill.