It was just a humble doubleheader split, but the Baltimore Orioles loved it while the New York Yankees were left to growl.

For the Birds - still in first place by a half-game - it was "mission accomplished" after lefty Rudy May got the best of it from troubled Catfish Hunter in the 5-1 opener.

Even though the Yanks came back with one of their trademark romps 2, in the nightcap, the Oriole damage had been done. The upstart Birds to this series, 3-2, and shoved the Yanks from first place to third in the process.

Many a Yankee flaw showed up along the way, especially in the rather slack twin bill that was better suited to a crisp 500-word dispatch than five hours watching.

Hunters was the Yankees' bad news while 153-pound southpaw Ron Guidry, who stopped the O's on four hits for 8 1/2 innings in the nightcap, was the blessing.

Hunter in his second season of battling tendinitis, looked like a once-great pitcher who now needs either a long rest, a shoulder operation, a new pitch, or new arm.

It was only a matter of innings before the Orioles ambushed him.

The Cat survived a barrage of rockets for the first five innings, allowing only a solo homer by Ken Singleton that hit the foul pole at the third deck in right in the fourth.

But in the sixth, the Birds broke loose.

Kiko Garcia lined a single and [WORD ILLEGIBLE] Bumbry laced the next pitch off Hunter's glove for a hit. Billy Smith blasted the first pitch 380 feet for a fly out, advancing both runners.

After an intentional pass to Singleton, Hunter played with rookie Eddie Murray's mind. His assortment of corner-nipping worked a 2-2 count, but Hunter's bait failed as Murray bumped a change-up on a line into right for two runs. It marked the third straight game in which Murray had driven in what proved to be the winning run.

Pat Kelly, who stretched his hitting streak to 18 games today (only two off the club record), followed with a single off reliever Sparky Lyle for a 4-1 lead.

That was enough for May, who has shown his feeling for the Yankees by beating them five straight times since they traded him to the Birds last June 15.

As in all three Yank defeats in this series, the New Yorkers found a way to make all the crucial outs in the close games. The Yanks actually outscored Baltimore, 26-18, in this marathon series, but the of clutch hitting cost them dearly.

May tossed his big curves to precise spots whenever the Yanks got a pair of men on. And each time - in the fourth, fifth and seventh - May got a pop-up or a double play.

The Yanks needed the second game badly to avoid four straight losses with Boston coming to town.Guidry, who looks like a skinny, bowlegged pair of tweezers, poured his fast ball past the Birds until Yankee Stadium's five o'clock shadow cut across in front of the plate and made his curve effective in the late innings.

The Yanks, only 5-12 against southpaws this year, played the long-ball bullies with rookie lefty Scott McGregor in the second game. Willie Randolph tripled 440 feet to dead center in the third and Graig Nettles followed by crushing a 2-0 cripple fast ball 420 feet into the right-field seats for a 2-0 lead.

The two weakest and least-used bats on the New York team knocked out McGregor in the sixth. Paul Blair (15 runs batted in for 375 at bats last year) wingled in one run. Mickey Stanley hit a bases-loaded single with two out for two more.

The Yanks have clipped a newspaper photo over Stanlty's locker that says, "Attention: Last action picture of Stanley in 1977." Stanley indeed seemed unaccustomed to reaching base, getting caught in a rundown the second he rounded first after his two-RBI hit.

The Bronx Bombers finished their cannonade with a three-run seventh off reliever Fred Holdsworth, who earned a "Squander" - the opposite of a save.

Perhaps more entertaining than either game was the unseen byplay all afternoon between managers Billy Martin and Earl Weaver, the Pair of Feisty ex-second basemen who love to taunt each other.

Weaver opened by drawing a big sign on his locker roon door, "Press-Media Is Welcome at ALL Times," complete with illustrations of musical notes and flowers.

Martin, who took down his "No Interviews" sign today, but no answer for that, but seconds before the first game he had ex-Oriole Elrod Hendricks call Weaver on the dugout-to-dugout phone and fib, "Hey, Earl. They just activated me."

Weaver raced to home plate to ask the umpires for the straight dope. All he got was a booing from the 43,285 New York fans, who razz him on sight, and word that he had fallen for Martin's gag.

In the final inning of the second game Weaver got the last laugh. With three victories here and first place in his grasp, Weaver sent the O's bat boy to Martin with a message.

"He told Billy," grinned Weaver, "it's all right to use Elrod now.