President Carter's attempt to head off enactment of a college tuition tax credit by increasing federal scholarships and students loans got a mixed reaction yesterday, with predictable praise from supporters but some opposition from Republicans and parochial school representatives.

The proposal generally won praise from witnesses before the House Education and Labor and Senate Human Resources Committees, but Bill Brock, chairman of the Republican National Committee charged that Carter was "hoodwinked" by Health Education and Welfare Secretary Joseph A. Califano Jr. into proposing the plan.

At the same time, Catholic groups appeared split over the measure. The 28-member Association of Jesuit Colleges and Universities endorsed the increased school aid, but some parochial school spokesmen expressed disappointment that it would not aid elementary and secondary school students.

Father Virgil Blum, president of a group called the Independent Catholic League of Religious and Civil Rights, issued a statement charging that dthe plan was "a renunciation of the President's campaign promises" to aid pupils who attend parochial schools.

Opposition of Catholic school group to the Carter proposal would not in itself be fatal. The parochial school forces might play a greater role in any tuition credit legislation. They want to extend tax breaks to parents whose children attend parochial elementary and secondary schools.

This version of the tax credit, sponsored jointly by Sen. Daniel Patrick Moynihan (D-N.Y.) and Bob Packwood (R-Ore) would cost the Tresury an estimated $4.7 billion by 1981 -- double the cost of a rival tax-credit proposal that does not include parochial schools, and far more expensive than Carter's plan.

Meanwhile, new buget estimates showed that the Carter proposals would cut into the administration's so-called "contingency fund" and leave less money available for the White House to use in its long-promised urban financing initiative this Spring.

The plan would require only a modest $215 million in actual additional spending in fiscal 1979, reducing the 1.7 billion allotted to the contingency fund to just under $1.5 billion. (The Carter plan would not actually begin channeling new monies to the nation's colleges until the fall of 1979.)

But measured another way, counting authority to commit funds for future years, the extra federal aid would trim the contingency fund more -- $1.2 billion from $3 billion allotted. The administration has not yet disclosed how much it had been planning to earmark for its urban program, but it does plan to use contingency monies.

The Catholic League's concerns about parochial school and were underscored at yesterday's hearing by Rep. Mario Biaggi (D-N.Y.), a newly announced convert to the Carter proposals. Biaggi read a statement from Catholic officials in his state expressing disappointment in the president's action.

Carter promised during the 1976 presidential campaign that he would propose steps to aid parents whose children attend parochial elementary and secondary schools. Califano told the committees yesterday the president still plans to fulfill that promise, but he did not say when or how.