Education Secretary William J. Bennett said yesterday that the Supreme Court displayed "a fastidious disdain for religion" when it ruled Monday that public funds could not be used to pay teachers in parochial schools.

Bennett said the decision was "a terrible decision" and added that the court's "disdain for religion" is "to me hard to fathom, hard to understand." Later he said that the ruling would not deter him from pursuing a plan under which parents of private-school children would receive vouchers to help pay for their children's education.

At a breakfast meeting with reporters, Bennett also criticized the National Education Association, which is meeting here this week. Bennett suggested that the NEA leadership may be far to the left of its members, and he said the powerful union should "get into education in a serious way" and out of national politics.

Bennett noted the NEA's strong support for Democratic presidential candidate Walter F. Mondale last year, and said "the membership of the NEA does not feel a political identity that's so obvious. Forty-five to 50 percent of them voted for President Reagan," he said.

"I think it would be good if the NEA leadership began to reflect its members."

Bennett's tough language comes as NEA President Mary Hatwood Futrell is trying to shift her traditionally liberal union to a more moderate stand on issues affecting the teaching profession. On Sunday, Futrell held out the possibility of a rapprochement with the Reagan administration, asking Reagan to "join the NEA."

Bennett said yesterday that he welcomes Futrell's "different tune." He said the change came because the union is going through "a period of identity crisis and trying to decide whether it's going to be constructive."

Asked whether he thought the NEA should stop endorsing presidential candidates, a practice it began in 1976 with Jimmy Carter, Bennett replied, "Maybe, maybe."

Some NEA members have introduced resolutions to allow rank-and-file members more say about endorsements in presidential primaries.

One resolution, introduced by the Georgia state delegation to the convention, said, "Early endorsement of presidential candidates has created division among our members."

The resolutions will be voted on today.

Bennett elaborated on his remarks later, at a news briefing to unveil a reorganization of the Education Department's research functions. Related story, Page A15.

At the briefing, Bennett said, "I think the decision was terrible. It was badly reasoned. I don't think it makes sense."

The court, in two opinions Monday, rejected use of public funds for remedial or enrichment instruction in parochial schools in New York City and Grand Rapids, Mich.

The ruling was seen as a defeat for religious groups that advocate public aid for their schools, for conservative groups and for the Reagan administration, which has been pushing for more public involvement in private and parochial schools through its proposals to give vouchers to parents of children in those schools.

Court observers said if the justices rejected use of public money to support only one specific program for disadvantaged children, it is unlikely they would support use of public money to help parents pay tuition to parochial schools providing a full educational program.

Bennett said he is reviewing the administration's voucher proposal to identify any possible objections of the court.

Gary Bauer, the department's undersecretary-designate, said the voucher proposal and a companion proposal for tax credits for private school tuition costs, would be introduced in Congress "by the end of the summer, hopefully. Sooner, rather than later."