Showdown on M Street: When George Thorogood and the Destroyer launched into "Madison Blues" in the second set at the Cellar Door. Thursday, it was a signal (relayed by the light man) for the Nighthawks, playing across at Desperado's to strike up the same tune. Midway through, Thorogood, guitar in hand, bolted out the M Street exit to meet Jimmy Thackery, also carrying his weapon. The two stopped traffic for a couple of minutes, never missing a riff, then kept moving - Thackery into the Cellar Door to join the Destroyers, and Thorogood into Desperados.

Cancel the Kristofferson Coolidge show scheduled for Aug. 11 at Cap Centre.

Anyone planning to crash Sunday night's rescheduled Fleetwood Mac concert at the Capital Centre should be forewarned. As soon as the show was postponed Wednesday, replacement passes were distributed to those in the sell-out crowd of 20,000 who had already thrown away their ticket stubs. However, Big Mac has been held over for a second show Monday night. Tickets for that are going fast too.

Washington's version of the Super Session, the Cheek-to-Cheek Allstars, are circling the town this weekend in what may be a one-time grouping. The Allstars, who include Catfish Hodge, Tom Principato, Bill Holland, and Thackery and Pete Ragusa of the Nighthawks, were scheduled to play Desperado's last night (with a look-in from Tim Eyerman); they'll hit Childe Harold tonight and Saturday. Bethesda's Psyche Delly on Sunday night, and the airwaves (via WHFS' "Take One") from the Sounds Reasonable studios Monday night.

RSO's in soundtrack heaven: "Grease" is still at No. 1. "Sgt. Pepper's Lonely Hearts Club Band" entered at 24 with a bullet, and even "Saturday Night Fever" is still hanging in - at No. 6 . . . More Fever: First John Travolta dropped in on Stevie Wonder's L.A. recording session to sing back-up, then both dropped in on an O'Jays concert for a little more vocalizing . . . And still More: Robin Gibb of the Bee Gees has recorded a disco album with Big Bird called "Sesame Street Fever" including a disco'd version of "Rubber Duckie" . . .

Duet of the Week: Elvis Costello and Delbert McClinton at McClinton's Lone Star Cafe Show in New York . . . According to the speechifying made at CBS Records' convention in Los Angeles, CBS Records Group revenues may hit the $1 billion mark this year. Incidentally, Washington's Walter Egan was among the CBS artists showcased for conventioneers.

WRC's Angela Owen will narrate the 8:30 p.m. Saturday "Jazz Nexus" program at The Eliipse depicting the development of the small band jazz sound from Dixieland through [WORD ILLEGIBLE] performers are Larry Banet and the Stentorian Jazz Band, and Musical Mandana, Roberta Washington's 12-piece Latin jazz band.

Sunday night (same time, same place) big band jazz development is traced by Swingworks, a conglomeration of D.C.'s best session and theater musicians.