No one can say the National League's two pennant races lack either symmetry or dramatic potential. The East and West look like mirror images of each other.

Both defending divisional champs, the Pittsburgh Pirates and Cincinnati Reds, got off to excellent starts but have done very badly since, each falling into third place with a record barely better than .500.

The fans of Three Rivers and Riverfront, those parks that look like huge, spangled steamboats, are worried about their perennial powerhouses. And with reason.

The parallelism between the divisions continues with the teams in second place, the Philadelphia Phillies and Los Angeles Dodgers. These rich clubs, chock full of All-Stars growing long in the tooth, met in the championship sereis of '77 and '78, but contracted terminal complacency last season.

Now, both the Phils and Dodgers have had shakeups, thanks to front offices that have vowed to squeeze another flag out of fresh mixtures of new no-names blended with the old brand names. The projects have been partial successes.

Finally, and perhaps most important, two long-spurned expansion teams that got into a pennant race for the first time last year -- the Montreal Expos and Houston Astros -- have used June to surge into first place. They may stick.

Traditionally, the baseball season before the All-Star Game is merely a preamble, with the serious business only beginning thereafter. This year in the NL, however, it seems possible that the most important clues to the whole season's mystery have already been shown to us.

The Pirates and Reds felt the hot breath of the Expos and Astros in last season's excellent to-the-wire September duels. In the offseason, the Bucs and Reds both lost free agents (Bruce Kison, Fred Norman, Joe Morgan) while their pursuers both made conspicuous additions (Ron LeFlore and Nolan Ryan).

So, Pittsburgh and Cincinnati felt the need for fast April blitzes. Forestall a case of the jitters. Show the new kids on the block who's boss. That sort of thing.

The Reds won their first eight games. The Bucs began June playing alomost .700 ball.

Then the holes in the hull started showing.

The reds leak worse, and may soon be sunk.

Cincinnati's Hall of Fame cornerstones are Geroge Foster, hitting .232, Dave Concepcion, batting .239, and Tom Seaver, who has a 3-5 record and is on medication for tendinitis in his right shoulder.

If that trio doesn't right itself, then the Reds, already seven games behind Houston in the loss column, may disappear.

The Pirates are made of sterner stuff, but they have plenty of problems, which could no longer be hidden when the Bucs lost nine of 10 in late June.

The hard-nosed, self-proclaimed Dirty Bucs look like one large black-and-gold bruise. Willie Stargell, hit by a pitch on Opening Day, has battled bone bruises, pulled hamstrings, creeping fat and age, while creaking to the plate only 145 times in 72 games. Even if named to the All-Star team, Stargell has announced he won't go. He's too banged up. Dave Parker, a play-with-pain type, has a chronic bad hand, bad knee, bad shoulder and (for him) bad stats of just eight homers and a .280 average.

It it isn't Tim Foli going on the 15-day disabled list with an infected shin from too many spikes, slides and foul tips, then it's Bill Madlock missing 15 games on a different sort of DL -- the Doghouse List for players who shove gloves in umpires faces.

Luckily, the Bucs have a magic position -- left field. Whoever they throw out there thinks he's Babe Ruth. The revolving quartet of Lee Lacy, Mike Easler, John Milner and Bill Robinson batted .470 over the Bucs' first 65 games when they played left.

Worse than hustle-type injuries is the Pirate starting ptiching rotation; cry babies Bert Blyleven (2-7) and John Candelaria (4-7) would tax any manager with their griping.

Fortunately, the Bucs are adept of miracle cures. Jim Bibby has decided at 35, to pitch with his brain instead of his 250-pound brawn, and has gone from career mediocrity to a 9-1 record.

The final two Pirate hurling spots are pure hold-your-breath. Right hander Eddie Solomon, acquired from Atlanta, has won four games, and "officially changed my name" four times as a Pirate. Formerly "Eddie," "King" and "B," Solomon currently wishes to be known as "Buddy." The Pirates just call him a gift from heaven.

Pittsburgh's No. 5 starter also has four names. So far this year, his name has been Jim Rooker, Don Robinson, Andy Hassler and Rick Rhoden. All have performed namelessly.

Despite their miseries, the world champions still have more charisma than all the Expos and Astros extant.

In August and September, if enough corsets, braces, tape and cortisone can be found, the Pirates may become a bit mystical. It ain't "family"; it's grit. Nobody in baseball trots out for the late innings of big games quite like this bunch. They shouldn't win, but they may.

If Pittsburgh and Cincinnati were adamant about early foot, then Los Angeles and Philadelphia felt an almost hysterical urgency to prove their worth quickly so that their massive, but fickle, constituencies would keep coming to the park in 2.5 million to 3 million numbers.

Both the Dodgers and Phils have, in a sense, already shot their bolt with their best big-name players having outstanding springs. And, like a fighter who throws his best punch only to see his foe smile, they have to wonder what they can do for a second-half encore.

The phils got 21 homers from Mike Schmidt and 15 from Greg Luzinski in their first 65 games, while Steve Carton is now 13-3. How do they top that? Or, perhaps, even match it?

Aside from Carlton, the rest of the Phils' starting staff -- including rookies Bob Walk and Jim Larson, dismal Randy Lerch (2-10) and Dick Ruthven (already banished to the bullpen once) -- has a total of three complete games.

A merely modest Phil bullpen has contributed to an 11-14 record in one-run games. This club may be looking for a soft spot to fall.

The Dodgers have had unexpected good fortune, so far, on a comparably grand scale.

Dodger sluggers have hit as well, or better, than ever, even those thought to be deceased like Dusty Baker (18 homers already, after averaging 17 the last two years) and Reggie Smith (hitting .335 with more at-bat s than he had all last season).

Three trading-block hurlers who were in total disrepute, but were virtually worthless on the offseason open market -- Jerry Reuss, Bob Welch and Don Sutton -- have gone from 24 to 35 in '79 to 22-5 in '80.

Because pitching depth so often is the factor that opens big league leads, or provides the basis for large comebacks during the dog days of July and August, the National League team with the best chance to have matters in hand by Labor Day may be Houston.

If the Astros aren't well-suited to the next 60 days -- a staff with heat for the heat -- then who is?

The Astro team ERA was 2.70 (until Atlanta scored 27 runs in the last two games), with J.R. Richard, Joe Niekro, Ken Forsch and even Vern Ruhle (5-1) all looking like winners. Houston is 26-11 at home, having ripped off winning streaks of 14 and eight games in the Astrodome. Nolan Ryan, of course, is having his typical :500 mystery season, million-dollar contract or not.

When Richard, with his 1.75 ERA, throws his bullets, the signs go up in Texas saying, "You can't shoot our J.R."

With young righty Frank LaCorte (0.61 ERA and 11 relief points) paired with Joe Sambito in the bullpen, with 80 team steals already and with the league's best fielding percentage, the Astros look extremely ready to win.

All the small, but symbolic, touches have gone Houston's way. Joe Morgan has worked out as a solid second baseman and team leader. The Astros have 36 homers, although 26 have been bases-empty jobs, after just 49 all of last year. In fact, the lucky Astros have had only one injury all season and that was to Art Howe who, after missing two days with a broken jaw, immediately came back with a wired jaw and a plexiglass face mask and has hit .320 since.

If the Astros' excellence eventually defuses the excitement in the West, then the universal absence of solid pitching in the East -- even with the once strong-armed Expos -- should ensure at least one late-season NLrace.

It may be a dead heat between Philadelphia, Pittsburgh and Montreal as to which has the most pathetic fourth and fifth starters. This was the year that Bill Lee could have made himself the hero of Quebec. His left arm was desperately needed in Montreal. So what does the Spaceman do? He goes jogging at 2 a.m., gets scared by a black cat that jumps in his path, trips into a wrought-iron gate, and sends himself to the hospital with a badly bruised hib and abdominal injuries.

At least, that's what Lee says.

Think that's not an omen?

Last season, Lee was jogging and got side-swiped by a taxi.

Montreal brass flinches at the mere mention of his name. General Manager John McHale greets Manager Dick Williams by saying, "Don't tell me. Lee was out jogging and got run over by a submarine."

In the end, the East probably will not be decided by the glamor lineups in Pittsburgh, Philadelphia and Montreal. When the disabled, like the Expos' Ellis Valentine and Larry Parrish, and the lame, like Stargell and Parker, finally pull themselves together for the stretch drive, the crucial difference may well be elsewhere.

Pitching tells the tale. At the moment, only one team in the National League can look to the mound with confidence -- Houston.

As for the rest, counting on names like Walk, Larson, Solomon, Lee and Leibrandt as crucial starters, the decisive factor may be which pitching coach can keep his collection of klutzes away from those taxis, black cats and submarines.