On baseball's opening day, when the scheduled game time is only a guess and when a president or governor is liable to show up and want a nice seat in the dugout, it's important that a starting pitcher have composure.

Two years ago, Scott McGregor admitted he lost his. A year ago, Storm Davis said it was a problem.

For the Baltimore Orioles' 1986 opener Monday at Memorial Stadium at 2:05 p.m. against the Cleveland Indians, Manager Earl Weaver has chosen Mike Flanagan.

"He's a veteran," Weaver said, "and he won't let all the hype bother him. He's been through this kind of stuff before."

More than that, at 34, Flanagan has become the heart and soul of the Orioles' pitching staff, the person other pitchers confide in and the one they go to for advice.

He also has had a remarkable run of wonderful and awful luck since his last opening day start in 1978, and along the way, has learned more about composure and patience than he's likely to need for a while.

He won a Cy Young Award in 1979 with a 23-9 record and followed that with a 16-13 record in 1980. That wouldn't be so remarkable except that he's the last American League pitcher to follow a Cy Young season with so much as a winning record.

His run of good luck pretty much ended there because he suffered from a sore left shoulder in 1980, tore a forearm muscle in 1981, wrecked a knee after a 6-0 start in 1983 and, last winter, ruptured his left Achilles' tendon.

At various times, he has pitched with a sore arm, with heavily wrapped legs and with a 10-pound knee brace. But when he underwent surgery to repair the Achilles' tendon, doctors told him: We'll see you next spring and then decide what kind of career you have left.

A year ago, when Davis was opening for the Orioles, Flanagan had just begun to walk and was doing therapy in a swimming pool. He had joked about retiring so many times that he now saw black humor in almost everything he did. In the swimming pool, he was working on an underwater changeup.

Worst of all, the game he was going to divorce was about to walk out on him first.

He laughed, but he brooded, too.

And he worked. He became a disciple of Cybex machines, ate more chicken than steak, and when he returned July 20, barely resembled the previous Mike Flanagan. The soft upper body had been replaced by one that was defined and hard. The fast ball that had faded steadily for three years was back -- ticking 90 mph at times -- and the arm that was once the pride of the Orioles' system was rested and strong.

Today, as the Orioles held a team meeting, tried on uniforms and took batting practice off the machine beneath Memorial Stadium, Flanagan stayed for an hour as wave after wave of reporters came to interview him. He laughed about his Florida tan, a spring temper tantrum by Weaver and his other opening day start, in 1978, when a Weaver brainstorm had Eddie Murray at third base.

"Probably only a World Series or playoff game is more exciting than opening day," he said. "It's a lot like those games because you don't know when it's going to start, so it's difficult to warm up."

Flanagan's may be the best, but it's just one of the remarkable stories the Orioles have at the beginning of this 1986 season.

Another is the little manager, Weaver, who was playing golf in Miami when the Orioles beat Texas, 4-2, to begin the 1985 season. When Joe Altobelli was fired last June, Weaver was rehired for the final 105 games of 1985, and although he's making no commitments, already has talked about plans for 1987.

"The butterflies will be there on the way to the park," Weaver said. "I know there's going to be a few games you go home embarrassed by the other team, but you don't want this to be one of them."

Another odd story is John Shelby, who is starting in left field. On opening day last season, Shelby came to Memorial Stadium, but didn't even bother to dress.

"I knew what was coming," he said.

What was coming was awful for one of the quietest and most respected of all the Orioles. After hitting .209 the previous year and after seeing the Orioles sign free-agent center fielder Fred Lynn that winter, Shelby was sent back to Class AAA Rochester, and some in the organization didn't know if he'd get back.

He was brought back June 7, homered off Milwaukee's Peter Ladd in his second at bat and New York's Dave Righetti in his third and hasn't looked back. He finished 1985 with a .283 batting average, seven homers and 27 RBI in only 205 at bats.

This spring, he was supposed to be a fourth outfielder and pinch runner, but he has hit so well the last two weeks -- 10 for 14 in one stretch -- that Weaver will start him in left field and use regular left fielder Mike Young as a DH.

This is also a resurrection day for Jackie Gutierrez, who is starting at third base in place of Floyd Rayford, who is on the disabled list with bone chips in his left thumb.

Gutierrez had a bad 1985 season, first getting hurt, then losing his job, then getting traded from the Boston Red Sox to the Orioles. After that, he went to winter ball and was released from two teams because of odd behavior. He says now that he was very depressed and that he is better, but the Orioles were concerned enough that they asked the American League office to reverse the trade (the league refused).

Regardless, Gutierrez came to spring training, and while hitting only .217, played terrific defensively.

With Shelby in left and Gutierrez at third, the Orioles are starting perhaps their best defensive team. Their pitching has looked terrific the last two weeks, and with the club again hitting homers in bunches (28 in 29 spring games), they're stopping just short of making predictions about '86.

The season also will begin in four other cities today, with Philadelphia at Cincinnati and San Diego at Los Angeles in the National League, and Boston at Detroit and Milwaukee at Chicago in the American League.