PASADENA, Calif. (AP) _ Twirling briefcases, chain saws, ironing boards and sometimes each other, the truly tasteless and the merely fun-loving joined in the 10th Occasional Doo Dah Parade, a send-up of the Tournament of Roses.

Police estimated 200,000 people turned out Sunday to watch such old favorites as the precision briefcase marching team and the Texas Chainsaw Massacre Drool Squad.

Squeals and roars of delight greeted the chainsaw marchers as they squirted fake blood and one drool squad member hung convincingly suspended from a meathook.

''The chainsaw guys are too real,'' said Vita Rachel, 31, of Pasadena, a 10-year Doo Dah watcher. ''But kids love gory stuff.''

''Bad taste knows no bounds, and the Drool Squad is certainly proud that without a doubt, it is the most tasteless group in the parade,'' said Don Coursey, who marched covered in mock blood and bits of fake flesh.

Coursey, a 31-year-old salesman from Huntington Beach when he isn't drooling, said he concocted the Chainsaw Squad one night five years ago when he was not altogether sober.

In fact, the idea for the Doo Dah Parade itself was born in a bar. The first was held Jan. 1, 1978, as a spoof of the tradition-bound Tournament of Roses parade held each New Year's Day. This was the tenth parade because one year folks liked it so much they held it twice.

The Doo Dah was the first of two big parades for Southern California on Sunday. The Hollywood Christmas Lane Parade, with an assortment of stars, made its way down Hollywood Boulevard Sunday evening.

The Doo Dah event featured a motley assortment of nearly 140 offbeat drill teams, bands and marching units, including stray collections of belly dancers, nude beach advocates and the Terrorist Kazoo Band.

''Nobody is safe,'' said Joe Messinger, a local real estate salesman and grand marshal of the parade. ''It's just a chance for grown-up people to bring out the kid in them.''

Competing with the chainsaw squad for unofficial ghoul honors were the Return of the Living Dead Mousketeers led by Michael Farkash, a suburban newspaper editor from the San Fernando Valley.

''The Mousketeers aren't dead,'' a pasty-faced Farkash said as he adjusted his decaying mouse ears. ''They're just resting.''

The precision briefcase team with its gray flannel executives was followed in the parade order by a team of marching briefcases twirling toy executives.

Then there were the cardboard cutout Southern California Rapid Transit District buses that handlers bumped into each other, inflicting mock injuries on innocent bystanders. The RTD has been under fire recently for several highly publicized accidents involving its buses.

There also was a collection of marching milk cartons, each with a face on it of someone or something supposedly missing, including Theodore Cleaver, the title character of the old ''Leave It To Beaver'' television series, President Reagan, and Lt. Col. Oliver North's files from the Iranian arms fund transfer.

The Marching Leech Kazoo Band made its fifth appearance, with 40 marchers wearing rubber masks that gave them a rather sluggish appearance. They pulled a facimile of ''The African Queen,'' complete with an effigy of Humphrey Bogart, who was covered with leeches in a scene from the movie about the African riverboat.