Just a few hours ago, the Montreal Expos were the first-place darlings of baseball and the beloved heroes of this suddenly baseball-crazed town.

Now, they are desperate.

When this evening began, all that Montreal could talk about was the way its Expos had won 18 of 21 games, including 16 of 17 in one splendid stretch, to move one tiny percentage point ahead of Pittsburgh in the National League East.

Now, after just one little heartbreaking 2-1 loss to the Pirates tonight, the Expos are looking down the barrel of a gun. Make that a cannon.

Although the final throbs of the season have 13 days to run, the Montreal year may come down to one day. If the Expos can't beat the Bucs here in Olympic Stadium on Tuesday night, their gutty number may well be up.

On this evening, Pittsburgh, which has won 16 of its last 21 games, followed a simple spoil-sport scenario.

The Bucs' 22-year-old Don Robinson, a 6-foot-4 231-pound bear of a right-hander who has had a sore shoulder much of the year, pitched an almost overwhelming six-hitter in which he got the final 14 outs on only 14 Expo hitters.

For offense against Montreal's perpetually star-crossed righty Steve Rogers, Pittsburgh got a pair of RBI singles by Dave (Cobra) Parker. Both hits were snaky ground balls that trickled into right field tormentingly.

Those who know Rogers (13-10) (WORDS ILLEGIBLE) the best unknown pitcher in baseball -- the man who absolutely never (WORDS ILLEGIBLE) any runs to work with -- will realize how appropriate it is that he moved into the major league ERA lead tonight (2.78) on an evening when he lost a pennant-race jewel.

In the morning standings, it will appear Montreal is merely a game behind -- and actually tied in the lost column.

But, as Expo Manager Dick Williams said, "This team has to face the worst streak of brutal schedule that I have ever seen or heard of in baseball."

Before tonight, the Expos had survived two doubleheaders in two days, splitting each with St. Louis. After finishing this two-game series with the Pirates, they once more face back-to-back doubleheaders in New York.

That's just the start. After three games in Philadelphia, the Expos must visit Pittsburgh for four games in three days, then jump to Atlanta for a one-day makeup doubleheader.

Think of it. In 13 days, Montreal will have played 19 games, including six doubleheaders. When they leave Olympic Stadium -- where they have a staggering 55-22 record -- the Expos must tackle a nine-day road trip with 13 games. Away from home, Montreal is 32-36.

So, it's simple. By any standard sense of baseball reasoning, Montreal needed a sweep here to give its beleaguered pitching staff breathing room. Even a split in this home park that they relish is a minor disaster.

To be swept was unthinkable. But now, as Bruce Kison prepares to face Montreal's top winner Bill Lee (15-10), the Pirates are thinking that thought and licking their chops.

"I'm not worried about the pennant race," Lee said, casually. "I'm worried about the human race."

More to the point, but no less in character, the Spaceman adds, "We're like the Bay of Fundy. Everybody keeps thinking the tide has gone out for us, and they write us off. And every time, we come back in."

In many ways, this Expo defeat, agonized over by a crowd of 54,609, had the ambiance of an Expo win. After all, Montreal has a whopping 38 come-from-behind victories this year. The Pirates have 39.

Rogers grimly kept the Expos in the game. After escaping a bases-loaded jam in the second inning, Rogers gave up the first Parker RBI hit in the third. In the fifth, the Cobra struck again, his hopper missing the gloves of Tony Perez and Dave Cash by inches for a 2-0 Buc lead.

Who should score that winning run from second but Pirate pitcher Robinson, the burly flamethrower who reached with a single. The youngster, who looks like a grizzled vet on the mound, barely beat the throw from right fielder Ellis Valentine with a fall-away slide.

That one play captured Montreal's excruciating margin of defeat, the hair's breadth by which they always seem to say behind the cocky Bucs. Expo catcher Gary Carter, forced to short-stop Valentine's handcuffing rocket throw, was in an awkward position and could not make the crucial sweep tag, even though he had the ball in his glove before Robinson arrived.

Rogers with typical grit, fought out of another bases-loaded scrape in that fifth, then, in the seventh, got out both Parker and Willie Stargell with a man on third.Little good it did him.

Rugged as Rogers was, the strapping Robinson always one-upped him. Robinson was in only two jams, and both times Rogers helped him get out.

Rogers grounded out with two on to end the second inning. After a Larry Parrish double and Rodney Scott single, plus Imar Moreno's run-scoring bobble in center, had plated the Expo run in the fifth, Rogers was asked to sacrifice-bunt Scott from second to third with none out.

Since the subsequent Expo hitter Warren Cromartie, singled, the game might be 2-2 yet had Rogers gotten the bunt down. But his attempt was too hard, and first sacker Stargell gunned down the swift Scott sliding into third.

After Cromartie's hit, the Expos managed only one scratch hit, which was immediately erased by an aborted steal.

Slowly, inexorably, the stadium became silent as Robinson -- the hitter, the slider, and, above all, the pitcher -- steamed in his fast balls and sliders.

In just 2 hours and 28 minutes, Expo jubilation had turned to Expo desperation. The road ahead for Montreal is rugged -- perhaps the worst stretch-run Baja in the game's history.

This is Montreal, calling the Spaceman. Come in, Spaceman. Please.

Robinson went the distance the fourth time this season, striking out four and walking two.

Pittsburgh manager Chuck Tanner, protested the game after a third-inning argument. Willie Stargell was charged with unintentional interference when his bat hit the glove of Montreal catcher Gary Carter.

On the play, Parker stole second. Plate umpire Doug Harvey sent him back to first because of the interference. Tanner withdrew the protest after the Pirates won.