The Carter administration is now claiming credit for a pending billion-dollar increase in federal aid to education for next year which it was opposing just six weeks ago.

Appearing here before the year's largest gathering of teachers, Vice President Mondale today praised the administration for making "the largest increase in federal dollars for education since the Elementary and Secondary Education Act was passed in 1965." The act is a cornerstone of federal aid to education.

Mondale told the annual convention of the National Education Association that President Carter supports a 15 per cent increase in education spending included in the Labor-Health, Education and Welfare appropriations bill passed by the House and Senate recently. Carter until recent weeks had opposed many of the increases, which represent almost a billion-dollar boost over the budget he proposed earlier this year.

The increases, Mondale said, signaled a marked change in attitude in the Carter White House from the Nixon-Ford years, which he called "one of the most anti-education administrations in history."

The NEA, the nation's largest teacher organization with some 1.3 million members, broke with its long tradition of neutrality to endorse Carter last fall, and this week repeatedly has credited itself with making "a critical difference in an election so close that it could have gone the other way."

But if teachers were looking for clear new directions in education policy from the Carter administration. Mondale didn't give them today. He pointedly ignored NEA's three main pet projects: establishment of a new Cabinet-level department of education, ennactment of a federal collective bargaining law for public employees, and raising federal contributions to education to 33 per cent of what it costs to run the nation's schools. The federal government now contributes about 7 per cent.

And when Mondale's longtime mentor and fellow Minnestan, Democratic Sen. Hubert H. Humphrey, called the Vice President to the podium and declared that establishing a new department of education is "long overdue," he received a thundering standing ovation from the 7,785 delegates attending the four-day gathering here. "A secretary of education could concentrate solely on the problems of education and not be bogged down with the crushing problems of health and welfare too," said Humphrey, who received MEA's Friend of Education Award.

It would also "signify the importance this administration attached to education." he added.

The only mention Mondale made of the proposed department which Carter said he supported in the campaign but which has run into opposition from HEW Secretary Joseph S. Califano Jr., was to tell an airport press conference that the matter was "under study" as part of the Carter administration's plan to reorganize government.

All week top NEA leaders had quietly hoped for even a brief mention of the department by Mondale, in part ot justify their strong and controversial push to press for a Carter endorsement last fall.

But they did not appear overly disappointed today. Stanley McFarland. NEA director of government affairs said. "We've talked to Carter. We've talked to his aides. What we're really interested in is what will happen in the next eight or nine months as the reorganization plan is formed."

Carter's budget initially called for $9.1 billion for education ($9.5 billion was spent in fiscal 1977) and an elimination of the direct student loan and impact aid program, which funnels dollars to areas with federal exployees. Despite early threats of a Carter veto, the House raised that amount to $10.2 billion on June 17. Last week the Senate voted a slightly smaller amount.

THe feeling among NEA lobbyists was that Mondale was claiming administration credit for something it didn't do and almost had thrust down its throat. "We know that," one staff member said. "But most of the teachers who heard him out there don't know it. It makes the administration look good to them."

The Vice President did make it appear that the spending increases were the administration's doing. At one point he said. "We've turned around the education budget.