The audience blew it.

"I feel inadequate to compete with little Amy or the witch doctor," John Anderson said to the Cable News television camera last night in Constitution Hall, after President Carter and Gov. Reagan had invoked those entities in their faces in Cleveland.

And the audience broke up. Whooping. Laughing. And Anderson broke up, grinning the kind of sly grin you grin when you're trying not to laugh, and that just made it worse.

Or better, depending on how you felt about the way the League of Women Voters ran their two-thirds of the presidential debate in Cleveland.

Last week, Cable News' Washington bureau chief Stuart Loory offered Anderson the chance the League had denied him: a share in the presidential debate. "A great adventure," Loory called it last night while four producers out in the video trucks readied four videotape recorders to capture the statements made in Cleveland, then delay them while Cable News spliced in Anderson's statements and rebuttals, then switch back to Cleveland after the tapes had been rewound, while a stenographer listened to the live debate and wrote down the questions which were then hand-carried out to Daniel Schorr, who moderated the Anderson version.

And that was before it really got complicated.

Loory tried to think of everything: "I woke up and saw the debate set on the 'Today' show, and I noticed the blue trim on the lecterns, so I sent somebody out for some blue trim for ours. Of course, Carter and Reagan will be speaking from behind the Secret Service podia -- they're symbols of great power, they wrap them up in felt when they travel with them. And we've got that," he said, pointing to a plain old wooden model that did not, as the Cleveland ones did, have that look of being able to, say, achieve orbit or fire lasers with the push of a button.

And, as Loory said, "One of the things that's important is audience decorum. We've printed 3,758 tickets, and the League has only 750 people in a 3,000-seat hall."

And of course Howard K. Smith, in Cleveland, cautioned them all to be quiet as fair-minded little mice.

That wouldn't have cut it in Constitution Hall, where Carlos Van Leer, 73, a "Gray Panther activist" strolled the aisles with his accordion, singing "Who's Afraid of Anderson," apparently in support of him.

He stopped playing just in time for the audience to watch the introductions in Cleveland. Barbara Walters received a somewhat more ardent hissing from this crowd than Ronald Reagan.

The crowd ranged from outspoken Anderson backers, such as Laura Kahn and Reed Travis of Arlington, who said, "We think he's been murdered by the press," to people who were curious about this strange idea of electronically wedging John Anderson into the debate in cable TV households across the country (plus others, depending on whether conventional stations picked up the cable version).

Said John Hummer, a patent agent from Reston: "It's a considerable thing in TV history."

And for some it was already a nostalgia trip. Barry Bogage, a researcher at Congressional Quarterly, looked mournful as he said he was "a very early Anderson supporter. I gave $25 to his campaign six months ago. This morning I filled out my absentee ballot. I went for Carter."

Things haven't gone well for the Illinois Republican congressman, who has watched his fortunes as an independent decline. His campaign has been plagued with underfunding and an oversupply of bad luck: lost buses, rain on their solar panels and other glitches.

And minutes into the debate last night, cable viewers -- and the Constitution Hall crowd who watched on a big screen on one side of the stage -- got treated to the first of several awkward silences as the audio failed, then came back out of synch, followed by an apology by Schorr, then a cut to an answer by Reagan to a question that hadn't been asked yet in the cable version, followed by Schorr toting up all the damage and telling Anderson: "We lost the minute we owed you in a rebuttal of the statement on inflation, so would you like to take that," which he did, until Schorr interrupted with news that they were "having difficulty with the tape feed . . . "

It's amazing, actually, that Anderson wanted to get into the debate at all, much less in a format which wasn't even rehearsed until 7:45 last night. After his debate with Ronald Reagan in Baltimore, his standings in the CBS/New York Times poll fell from 19 percent favorable impression/24 percent unfavorable, to 20 percent favorable and 31 percent unfavorable.

He had even called himself "the Stealth candidate" at one point, pointing out: "I don't even show up on the Carter radar screen."

So last night, when it started getting rough out there in Cleveland, as Reagan took to comparing Carter to a witch doctor, and Carter replied by talking about his daughter Amy, maybe something sprung happily loose in Anderson, and he got up and admitted it, as much as conceded defeat of some kind, when he said he couldn't compete with that.

The audience didn't help either, by laughing so hard. Everybody had a good time, for a change. And nobody said they're rather be in Cleveland.