Two Years ago, the American people had lost confidence in the politicans who directed the nation's affairs. There was a deep, emotional demand for a new leader who could bring some fresh air into Washington's polluted backrooms.

Out of Plains, Ga., came Jimmy Carter, a man with a compelling smile, an engaging manner and a gift for reducing great issues to simple moral principles. He brought with him a coterie of associates.

The first to fall was his blustery budget director, Bert Lance. On the morning Lance faced his Senate inquisitors, he dropped by the Oval Office for a quiet prayer with Carter. Afterward, the president told me aggrievedly: "If we could have named 2,000 different things that might have caused me any problems or any embarrassment, Bert Lance's character would have been the last thing we would have guessed about."

The Lane affair was followed by David Gartner's appointment to serve on the Commodities Futures Trading Commission. After he was sworn in, the press discovered he had accepted gifts of stock totaling $72,000 from a major commodities dealer who would come under his regulation. Carter confessed at a news conference that he wanted Gartner to resign, but the new commissioner has hung on.

Then Carter's adviser on drug abuse, Dr. Peter Bourne, departed in a cloud of involvement in a Washington cocaine party and the falsification of a drug prescription.

Next the outspoken Midge Costanza resigned as the president's $56,000-a-year assistant after creating controversy and consternation as the White House liaison with such neglected groups as the gay-rights movement and the pro-abortion militants. She left professing her admiration for Carter but with the admonition: "For God's sake, where's the sensitivity?"

Now Carter is in the process of sawing another limb from under himself with an ill-advised appointment. On Capitol Hill and within the White House itself, the nomination of 46-year-old Alvin H. Gandal as commissioner of the Postal Rate Commission is viewed as a new potential disaster.

Gandal is an earnest, likable postal-service official who was fond of playing high-stakes poker in his off hours. With little political backing, he applied late for the job as head of the agency that sets postal rates for big mail-order and other business users.

On the basis of his first-hand knowledge of the Postal Service since 1969, Gandal was picked by Carter to everyone's surprise. Indeed, no one was more surprised than the nominee. "I was very honored," he told us.

Now eight months later, a Senate confirmation committee is balking at his appointment. The senators have two objections.

The first stems from Gandal's poker-playing. He admitted to committee investigators that he had been arrested in 1975 on a gambling charge for "participating in a noisy poker game." He posted $10 collateral with the Washington police after being arrested in Room 509 of the Statler Hilton Hotel. Government files report that "several thousand dollars had changed hands during the course of the game."

In two interviews, Gandal candidly admitted to our associate Gary Cohn that he had been a poker player off and on for 14 years. Most of the games, held in Washington hotel rooms, ran to hundred-dollar stakes. He told Cohn that he occasionally would win or lose several thousand dollars at some sessions. Over the long haul, he said, he probably broke even.

The confirmation committee is troubled by the fact that the White House knew in advance about Gandal's poker proclivity from information he volunteered to the FBI during a background check. But he insisted he swore off poker two years ago and does not engage in any other forms of gambling.

But more troublesome is the fact that Gandal, at White House urging, approached businessmen he would regulate for support of his nomination. They included representatives of companies doing heavy bulk mailing, greeting-card companies and officers of four major postal unions. All would come under his purview as head of the rate-setting commission.

Gandal denied any conflict of interest in those conversations. "I know what's right and wrong," he declared. "I wouldn't put myself in that position."

Because of all this, Senate investigators have concluded that Gandal "is not suitable" for the job. Sens. Abramham Ribicoff (D-Conn.) and Charles Percy (R-Ill.) have sent quiet word to the White House that the nomination should be withdrawn.

Carter's people has maintained a studied silence or, in the words of a congressional source, "they're letting the guy dangle in the wind." But after eight months of waiting, Gandal wants to have his say in public. "I think I'm owed a hearing and a vote," he told us. He wants the senators "to look me in the eye, ask me their questions and judge me as a human being. I want to serve. I want to work."

Senate sources are less censorious of Gandal, meanwhile, than they are of the president who appointed him. They describe the appointment as another instance of White House inexperience and indecisiveness.