AFL-CIO President Carter Meany yesterday attacked President Carter as the most conservative chief executive since Calvin Coolidge.

In his most caustic critique so far of the president he helped elect two years ago, Meany accused Carter of reneging on major campaign promises, and said he was "very much" disappointed with Carter's performance.

Hardly missing an opportunity to point up his long festering dissatisfaction with Carter, Meany said he had no quarrel with a businessman as president, but then added, acerbically, "Why in the hell did he we have to have a small businessman?"

Meany's midterm assessment of Carter at a luncheon meeting with reporters followed weeks of low-key, even civil relations between Carter and Meany, despite their strong disagreement over inflation and dollar-rescue programs.

Relations between the onetime farmer-businessman from Georgia and the 84-year-old Bronx-born labor chieftain have never been good, but, as recently as last Sunday on CBS-TV's "Face the Nation" program, Meany went out of his way to blame their differences over economic matters on White House advisers rather than Carter personally.

But this was before the elections and before Carter signed the tax and energy bills, which the AFL-CIO had been urging him to veto. In any case, Meany quite clearly decided yesterday to speak freely - and appeared to enjoy it immensely.

In observing that Tuesday's elections point to a conservative trend in the country, Meany said Carter was the "most conservative president . . . in my lifetime," but then allowed as how it may be only since Coolidge left office in 1929. Asked about Gerald R. Ford, Meany said Carter is "more conservative . . . in lots of ways," but did not elaborate.

He accused Carter of "opting for unemployment" for the future and claiming too much credit for having reduced the jobless rate in the past, saying that most of the credit goes to Congress for expanding his economic stimulus program.

Meany accused Carter of reneging on a campaign endorsement of national health insurance, saying that he "should have been ashamed to sign" the tax bill after promising tax reform in the campaign, and said he "fliplopped" on energy policies.

"So his record is not good," said Meany. But "he does have a nice smile." Earlier, Meany alos gave him a lone high mark for his Middle East peace efforts.

As for Carter's anti-inflation program, Meany said, "All I know is there have been a few speeches made . . . and the response has been zlich." he said he believes "there are some people in the White House who think you govern by making speeches."

Meany defended the AFL-CIO's call for across-the-board economic controls as an alternative to Carter's voluntary wage-price guidelines, but acknowledge that it could take thousands more federal employees to enforce it.

Critical as he was of Carter, Meany could not come up with a likely challenger for 1980 who was more appealing to him.

He said he thought Sens. Edward M. Kennedy (D-Mass.) and Henry M. Jackson (D-Wash.) would make good presidents, but he said he didn't think they will run. He said California Gov. Edmund G. (Jerry) Brown Jr. would be a formidable opponent but, asked if Brown would be an improvement over Carter, responded, "No."

Looking at Tuesday's elections and other factors, he said Carter is in trouble in many of the states that were crucial to his 1976 victory.He said the Republicans' record for self-inflicted electoral wounds may be the "greatest thing Carter had going for him," but cautioned that Ronald Reagan should not be underestimated as a 1980 contender.

Meany acknowledged that organized labor "lost" in Tuesday's elections in terms of the prospects for labor legislation in Congress, and said he didn't know whether it would attempt to revive the labor law revision bill that consevatives killed earlier this year by filibuster.

But he said Missouri's defeat of a right-to-work initiative Tuesday may trigger union efforts to repeal similar laws in some of the 20 other sates that have them.

Meanwhile, Jerry Wurf, president of the American Federation of State, County and Municipal Employes, told a news conference that voters rejected the "meat-ax approach" to tax cutting in referendum votes Tuesday and hailed them for it. He reiterated his call for federal tax incentives to encourage states and localities to impose more "reasonable and rational" tax systems.