A mere week before opening day, the Oakland A's were scanning the want ads for real estate and, in some cases, jobs opportunities, given the general assumption that the team would spend the 1978 season in (a) Denver and (b) last place.

Four weeks into the season, the team is in (a) Oakland, and (b) first place, with the majors' best won-lost record. Clearly the manic soap opera saga of Charlie O. Finley's "Mustache Gang" is not yet over.

From 1972 to 1975 the A's were one of the most imposing threshing machines in baseball history, with an unprecedented three straight playoff and World Series triumphs. But them came free agentry, and the A's stars - who generally likened Finley to the flu, flew the Oakland coop. Most of those who stayed were traded.

But 1977 the A's were a patchwork creation of greenhorns, castoffs and rebels. The result was a dead-last finish, 381/2 games out, behind an expansion team, in the major's easiest division.

Cruel humor was irresistible. They were called the Oakland AAA's the Apathetics, the Gong Show of baseball. The Oakland Coliseum became Heartbreak Hotel. Attendance, never much more than negligible, was virtually reduced to walk-in traffic.

In October, the team was "sold" to Denver oilman Marvin Davis, amid universal sighs of relief. But then followed a preposterous series of events which came down to a contract with the Coliseum that Houdini couldn't get out of. Accordingly, opening day found the A's still in Oakland, to the amazement of all. This amazement soon blossomed into wholesale stupefaction.

The A's began 1978 with all the liklihood for success of the Children's Crusade, which their lineup resembled. On their 25-man roster are eight rookies and eight second-year men; six of their starting nine fall into these categories. Seven others are considered little more than retreads. "Give this pa ck of tenderfeet, has-beens and damaged goods three weeks." said the experts, "and Oakland will beg Denver to take them."

The no-name A's have had their three weeks, and all they've done with this time is compile an outstanding record out of opportunistic hitting and a pitching staff which defies reason.

The latter had been a matter of special amusement going into the season - the journeyman arms of Rick Langford, Bob Lacey and Dave Heaverlo dubiously bolstered by assorted castaways (Joe Coleman, Elias Sosa, Pete Broberg, Steve Renko) and wet-eared youth who by all rights should still be eating minor league food (John Johnson, Al Wirth, Matt Keough).

Batters around the American League began pricing new cars; this would be like hitting pinatas.

So far, it's been like hitting ball bearings. This discount mound crew went into the weekend leading majors wins (14), shutouts (four) and ERA - a spectacular 1.38.

The A's batting average was far more modest at .257, but is close to that of the mighty A's of 1972-75 and included four starters batting near or over .300, something the A's of old never managed.

But these are mere statistics, the droppings of reality. As always, the real story is not so much the A's as their owner, general manager, chief scout, paymaster, ramrod, guiding force and albatross - Charles Oscar Finley, who has done for the concept of team owner what Bobby Fischer did for chessmaster.

The remarkable new A's are largely the simple expression of his formidable desire to win once more, in a final, florid display of acumen, guts and manpulation which will establish him, not-oriety notwithstanding, as one of the great characters of baseball history. To comprehend the team, one must understand the basic Finleyian principals which have made the A's what they are (and aren't): Pride, parsimony and revenge.

Pride. It was Finley, almost single handedly, who formed the world-class A's from novice stock in the early '70s, and it is his driving goal to prove that this was no fluke, but an achievement he can replicate at will, given time and trading.

Parsimony. Finley treats dollars spent like years off his life, and however the team has done on the field, it always has trailed the league in salaries , staff personnel and player comfort. Young ball players may not be good, but they are both cheap and grateful - qualities Finley finds irresistable in athletes.

Revenge. The World Champion A's were literally dismantled by the advent of free agentry, a concept Finley regards as a personal affront. He has declared a vendetta of herculean proportions against this vile and inflationary virus, and the whole point to the new A's is that if such a low-rent conglomeration can outperform such checkbook heavyweights as the Angels, Rangers or Brewers, free agentry will lose its leverage and its credibility.

Beneath the seeming futility of this is an ingenious Finley hypothesis: That some clubs are so talent-heavy, one can fashion a quality ball club just from their excess. So far, this theory has been dazzingly productive.

The Pirates had loads of talent everywhere but third base. Finley, who uses a negotiation like a Luger, gave them Phil Garner. In return, he got a major hunk of Pittsburgh's farm system. The fruits of this - Tony Armas (.295), Mitch Page (.344) and Langford (2.13) - could start for most teams in the league right now.

Gary Alexander, Gary Thomason and Mario Guerrero, along with Heaverlo, Johnson and Wirth, were trapped on the Giants' bench or in its farm system. For the price of Vida Blue, Finley now has two consistent power hitters, three winning pitchers and a shortstop batting .346. Dave Revering (.257) and Mike Edwards (.322), late of the Redleg and Pirate minors, are other examples.

Finley's crackpot notion that many minor leaguers are simply major leaguers without portfolio, is working.