The playoffs are baseball's house of horrors, an elegant but frightening mansion where the floor can collapse at any instant or an old ghost leap from hiding.

No matter how confidently a team feels that its feet are on the solid ground of fundamental baseball excellence, that trap door can spring open. The alligators of the second-guess swim in the pool below.

No matter how well the psychological spooks and fears of a six-month season have been locked in a closet, they can jump out at the worst moment and stop the heart.

"Nothing's as scary as the playoffs," said Baltimore Oriole captain Mark Belanger, an old hand who will be starting his sixth playoff when the Birds meet California in Memorial Stadium at 8:30 p.m. Wednesday.

"Everyone on this team is nervous, because everybody knows that nobody knows what will happen -- especially because the first and second games are so crucial.

"There's always a sense between two teams of which is better. Nobody knows the game as well as the players. But, in a short series, I'm not sure if that makes any difference."

If a feeling of mystery surrounds any playoff opener, then imagine the perplexity here with two of the alltime unfathomable prima donna pitchers scheduled to do battle -- the Orioles' eight-time 20-game winner Jim Palmer agains the Angels' five-time 300-strikeout man Nolan Ryan.

"Mr. Palmer, at what time should I report for duty tomorrow?" asked O's reliever Don Stanhouse, Stan the Man Unusual.

"Arrive about the seventh inning," said Palmer, looking out from his locker at a hoard of reporters among whom Stanhouse had sneaked to conduct his own interview.

"And will you be throwing many sliders tomorrow," asked Stanhouse, knowing the slider to be the eternal bone of contention between Palmer and Manager Earl Weaver.

Palmer winced.

"Those are the ones you'll be catching," said Palmer, referring to Stanhouse's seat in the bullpen.

"Oooohhh," said Stanhouse, "lots of change-ups, huh?"

Many an Oriole would like to give Palmer truth serum and interview his unconscious at length, just as every Angel would like to know what makes Ryan tick, and often explode.

"I had trouble sleeping the other night," said Palmer. "I was dreaming of spiders. I usually go to bed about 1 a.m. Now Earl he goes to bed at 9:30 -- p.m., not a.m.

"I guess I could always give Earl a call if I have insomnia," said Palmer, pausing. "And he'd hang up on me."

The entire playoff may hinge on this odd and ironic first game meeting between super pitchers, both of whom probably should discard their numbers and wear "??" on their uniforms.

At present, Palmer, who raised a fuss a week ago by saying that Mike Flanagan should have the honor of pitching the first game, has warmed to the task so much that his mates are worried a bit.

"I felt the best I have in two months the last time out," said Palmer, contradictory as always, since he gave up six runs in that game -- his most in two months. "My arm feels fine."

"I hope Jimmy doesn't feel too good," said the O's Ken Singleton. "If there was nothing wrong with him I would be leery."

"When Palmer comes in after warming up, I hope he's bouncing his change-up in the dirt and complaining about everything," said the pitching coach, Ray Miller. "That means he's sure to pitch a shutout. If he's quiet and satisfied, I'll be scared to death."

It is Palmer's history that he is at his best under pressure, particularly against the highly praised Ryan, a media golden boy in California who has perhaps received more credit than his statistics would warrant while Palmer probably has gotten less.

"Jimmy likes to pitch against Nolan," said one Oriole. "In fact, what he likes to do is eat him alive."

While Palmer is 7-2 in postseason games, Ryan has a multitude of statistical hexes to overcome. He is 5-13 career against the Orioles, while Palmer is 21-8 against California. In two games against the Angels, Palmer posted a 1.26 ERA. In the same number of games against Orioles, Ryan's ERA is 7.50.

While Ryan always has pitched dramatically worse on the road, Palmer has a 2.28 career ERA in Memorial Stadium. Also, while Palmer's statistics in 1979 (10-6, 3.30) resembled a normal Gentleman Jim, who missed 17 starts, Ryan had an ERA of over 6.00 after the All-Star break.

"Ryan is still different than anybody else," said Singleton, who, like most hitters, would rather bite their tongues than bad-mouth the Ryan Express.

"We always seem to do all our damage against him in one inning. We get an error or a couple of walks and we build one three- or four-run inning. And that's enought.

"Last year, Pat Kelly hit a grand slam off him in the eighth to ice a game. I was up next. I just went up and calmly struck out. There's no reason to make the big guy mad."

Especially when Ryan, 16-14 in 1979, finds a way to lose more than half his games against contending teams.

The O's seemed relaxed, almost on holiday, yesterday, playing a five-inning "situation" game with Scott McGregor "beating" Steve Stone, 5-0.

"My guys are gonna be ready and Scotty's are going to be depressed," said Stone, Roud of the meatballs he had served up, including a homer to Rick Dempsey. "I got Dempsey so psyched that he's still standing in the shower taking practice swings."

In the clubhouse, the Birds yawned casually. John Lowenstein, who will start in left field ahead of Gary Roenicke, was wearing his "Dead Goat Saloon" T-shirt, while Flanagan countered with one from "GuadalaBarry's."

The Angels, accustomed to Anaheim, manicured grass and Disneyland down the street, took batting practice under gray skies and gaped at the muddy, football-striped and generally dismaying Memorial Stadium field.

Owner Gene Autry, in red cowboy boots and a gentle, grandfatherly mien, sat in the visitors' dugout, granting audiences.

"Can you take a four-minute ride in a buggy with a blond for Channel 2," asked a TV announcer.

"Does she look like Dolly Parton?" asked Autry, known for shrewdness.

This ballpark, and the streets leading to it, are a far cry from the way they looked in midsummer when the Orioles were announcing themselves to the baseball world.

Orange-and-black bunting, fresh paint and a general air of hurried construction pervade the park. Outside, the signs that say "33rd Street" have new, official-looking markers under them reading, "Oriole Boulevard."

Only the Birds themselves look the same. Tim Stoddard (1.71 ERA) has returned to form in recent days, completing a sense of general health despite Belanger's and Lowenstein's sore ankles -- that is new to the O's in '79.

By contrast, the Angels have lost Joe Rudi and Willie Aikens. Their No. 3 pitcher in innings (197), Jim Barr, broke his finger in the party celebrating California's clinching the West flag. He punched a toilet seat in glee and is out.

Even more sickly are the Angel batting averages against Oriole pitching this year: .235 overall. Don Baylor (.156), Rod Carew (.190) and Carney Lansford (.111) are the most anemic. Bobby Grich and Dan Ford, who each have 101 RBI, combined for one homer and six RBI in 81 at-bats against the Birds.

The only Angel regular who hit over .217 in those dozen head-to-head meetings was harmless No. 9 hitter Jim Anderson, who batted .318.

No team in 15 years has scored as many runs per game as the Angels, but much of that scoring was done early in the season when the Californians were healthy.

No team in more than 30 years has had a team ERA as superior to the league average as the Orioles, and most of that mark was built in the second half of the year as the staff grew stronger.

Those are the battle lines -- Oriole arms against Angel bats.

Throw in a couple of unpredictable psyches like those of Palmer and Ryan, and you have a house of thrills.

One which the Orioles, so superior statistically to the Angels all season, hope does not suddenly become a chamber of horrors.