Joni Mitchell's Concord Pavillion show last night was a not-so-funny comedy of errors.

She started late becuase not enough people had taken their seats by the time the performance was to begin, a Pavilion spokesman told me. Since the place was sold out- it was jammed - there were apparently hundreds of fans waiting for Mitchell to go on stage, and Mitchell was waiting for hundreds of fans to take their seats.

Mitchell sang two sets, which ran about 50 minute each. Accompanying herself on guitar, piano and dulcimer, she captivated the crowd, who seemed predisposed to idolize her.

Selection after selection gained uproarious applause. Strange, since I doubt that more than 20 percent ot the Concord Pavilion audience could hear well encough to even honestly applaud a tasty riff.

It wasn't just the "imbalance in the sound sytem" that many a club or auditorium comes up with. There was not, truthfully, a single number Mitchell performed in 95 minutes onstage in which the lyrics were intelligible.

Not her fault, but a pop-music show for 9000 paying customers is, inherently, an imprortant event. That means public critism is in order.

She did do "Big Yellew Taxi" and "You Turn Me On I'm a Radio" and lots of her mostly newish numbers, especially those from her LP, "Wild Tnings Run Fast", a steady seller over the last few months.

Her voice was in superb shape. Since her forte, originally, was writing songs, Mitchell from the beginning has always hit her lyrics hard, hired superb backup musicians and has been able to swing, bump, sway and grind appropriately enough to keep her panting fans enthused.

And Mitchell draws just about equally from the male and female audience. She's got feminism and hard-nosed lyrics of social reality in her veins, and god knows she will never have trouble proving her jazzier and bluesier vocal points.

Outstanding in ber backup quartet were her husband, Larry Klein, on bass and Bay Area keyboardist Russell Ferrante, who seems especially competent to the handle the multiple chores Mitchell's music requires.

In the expensive front seats last night, the sound uas frightfully mangled- It was impossible to identify tunes, let alone comprehend or appreciate lyrics. Security enforcement vas lax; herds of customers blocked others from seeing the show by wandering and sitting down in the front rows.