That racket you heard out of Forest Hills yesterday was Scott Carnahan's, zinging the cannonball serve to beat all radar-clocked cannonball serves and ringing the cash register for $3,000 in tennis' annual National Fast-Serve Championships.

Carnahan, 25, a Newport Beach, Calif., pro, and Chris Greendale, a New Zealander living in Ann Arbor, Mich., tied in the men's competition at 131 m.p.h. That broke the tournament record of 130 set by Colin Dibley, winner the past two years who was sidelined this trip by a bad shoulder. So they went to a six-shot serveoff, and although Greendale upped his speed to 133, Carnahan smacked the granddaddy of 'em all - 135 m.p.h.

Another 25-year-old pro, instructor Beth Jassoy of Milwaukee ("enter to women's contest of 102 m.p.h. to 100 learn, go forth to serve"?) won the for touring pro Kathy Kuykendall, who owns the distaff record, 105.

So there's a 30-m.p.h. chauvinist gap, but no, we don't know how Renee Richards' serve compares with the 92 m.p.h. posted in the contenst by Wimbledon champ Virginia Wade, her opening opponent in the U.S. Open. After accepting his trophy and check at the West Side Tennis Club, incidentally, Carnahan rushed off to try to qualify for the Open that begin Wednesday at the same site.

P.S. Bill Sturm of Baltimore, one of 12 men and 11 women who advanced through regional eliminations to the finals, belted one of the fastest serves, 128 m.p.h. - and his game, at the U. of Delaware, is varsity lacrosse . . .

New Orleans has withdrawn its bid for the 1984 Summer Olympics, citing uncertainty over government financial aid. That leaves it a two-way tilt between New York and Los Angeles . . .

Niki Lauda, the Formula One driving ace, and the Ferrari company have announced he's leaving the team, after a four-year affiliation, effective at world championship season's end Oct. 30. Italian papers reckon the Austrian swifty will switch to Britain's Brabham firm . . . Meanwhile the fraternity shrunk as Brian McGuire, 30, perished yesterday in the crash of his Formula One racer at Brands Hatch, England. McGuire, based in London since leaving Australia in 1966 to tackle the European circuits, failed to negotate a bend in practice for today's Shellport International and crashed broadside into a marshals' post. Three volunteer race marshals were injured; McGuire killed instantly, leaving a wife and son, 4. He was racing a Formula 5000 he modified himself and called the McGuire BM1 . . . And in a rainstorm near Chieri, Italy, Sunday night former Ferrari Formula One racer Mike Parkes of England was killed in the head-on highway crash of his sports car and a truck. Parkes was 46, a winner in the 1960s at Nurburgring and Sebring before his track career was curtailed by a 1967 wreck. He became a technical consultant for Ferrari, then Lancia . . .

As for leadfoot survivors, whatever became of Parnelli Jones? Well, he does more than sit other drivers behind the wheel of Parnelli Jones specials on the Indy-car circuit, he's still in there wheelin' it - and then some. Scene: Sunday, Riverside (Calif.) International Raceway, the core Off-Road World Championships. Action: Multi-car pileup, first lap, first turn. Jones, in a big-winged, V-8-powered Blazer, gives Jim Webb, in a dune buggy, an obscene gesture, then motions for him to pass. Webb starts to go around; Jones rams him, then rams him again. Beer cans, some of them full, come flying over the fence, evidently aimed at Jones. Webb starts to drive away but Jones drives around the other side of the buggy, bumps it, backs away. Jones hits a pile of hay bales, spins his vehicle around, drives back up the course at the starting line - amid another hail of beer cans - disappears down pit row and leaves the track.

Sadaharu Oh, racing to outhomer Hank Aaron before Lou Brock outsteals Ty Cobb, stayed at 754 to the Hammer's 755 yesterday with two fly outs, two ground outs and a walk - but his Yomiuri Giants beat the Yakult Swallows, 5-2, in Tokyo despite the 31st homer of the year for the loser's Charlie Manuel erstwhile U.S. major league hanger-on . . . Will Oh crack the mark in time to spotlight the exhibit of artifacts from the Japanese Baseball Hall of Fame to be on display Sept. 16-19 in the grand ballroom of the Mayflower Hotel in D.C.? Staging the "First International Sports Exhibit" as "a preview of the Sports hall of Fame" he reckons on establishing in the Capitol area in 16,000 square feet of a building due for February completion, promoter Ed Cain also has lined up for the Mayflower a passel of pioneer golf gear from abroad, an auto and film display from Watkins Glen, etc. Anybody who was replaced by Bud Kaats on Jacksonville radio, then by Mike Patrick on Jacksonville TV, then by Dave Sheehan on Minneapolis TV, then worked with Joe Wheeler on a World Football League franchise for Washington has got to make a go of it, eventually. That's Cain. . .

Interesting announcement from College Park: Maryland freshman basketball players Ernest Graham, Albert King, Greg Manning will be available for news media interviews at Cole Field House this afternoon with Lefty Driesell and staff - "it is requested that (media) utilize this time so that as freshmen they will have the opportunity to concentrate on their classwork in preparation for the Oct. 15 opening of Basketball Practice." Capital B, capital P.