Federal and postal union leaders who spent a lot of time, dollars and effort getting President Carter elected, are having second thoughts about the man they feel they helped get into the White House.

Although both sides are being cordially and correct, there is a growing feeling of tension - and mistrust - between the Carter camp, which now represents management, and the union chiefs, who speak for most of the bureaucracy's 2.6 million workers.

It is too early to talk about a break. Most of the union leaders, for personal and philosophical reasons, would rather take their chances with a Democratis President and Congress. But they aren't happy with the way things are going, and some beleive the worst is yet to come.

Postal leaders generally are upset that the President hasn't endorsed their plan to revitalize the U.S. Postal Service with more public money, and a new Postmaster General who is and less like a "reasonable" politician and less like a chairman of the board.

The chiefs of unions representing both white collar and blue collar civil servants don't like the looks of plans the Carter administration has to revamp the systems used to pay their members, and to "streamline" government.

One carter proposal would make drastic changes in the way the half million wage board (blue collar) workers are paid, on grounds that they already make more than their counter-parts in private industry. Another would take 600,000 clerical and technical civil servants off a national wage scale, and tie their salaries to prevailing hometown industry rates.

The White collar union leaders are also worried about a proposal the White House is considering that would crank in the salaries of 12 million state and local government workers when October pay raises are fixed for U.S. civil servants. Although administration officials say it could mean higher annual pay raises for white collar government employees in some jobs, the union leaders fear the overall impact would be to decrease percentage increase for federal workers.

This month, the Public Employee Department of the AFL-CIO warned the Carter administration to go easy in selling its government reform plan by making it appear that federal and postal employees have it better then most workers in private industry.

The PED represents 30 unions with a combine membership of nearly 2 million. An editorial in the PED newspaper says . . . "Although not yet openly critical of President, Carter, federal and postal union leaders are concerned that recent actions by administration officials could lead to renewed public opinion attack against public employees."

The PED says the the administration is taking "hard-line position against federal white collar and blue collar workers . . ." The PED also is concerned that the President, in statements and attitude, is making it more likely that the U.S. Postal Service management will be very tough in contract negotiations for an agreement to replace the current, generous contract which expires in July.

One federal union president said that while the Carter people have gone out of their way to be nice to organized labor organizations that represent the federal work force.

"We aren't going to break with him," he said. "But if you wrote something to the effect that we are nervous, and nearing the boiling point, nobody would quarrel with that. If we have to spend the next few years fighting to keep what we, have rather we both have a problem on ourous, and nearing the boiling point, no-than improving things, you could say hands."