MARIJUANA AND PRO BASKETBALL -- A special report.; N.B.A.'s Uncontrolled Substance.
National Basketball Association players, former players, agents and executives say that contrary to wholesome image marketed by league, 60 to 70 percent of its 350-plus players smoke marijuana and drink excessively; two decades ago, league nearly collapsed under perception that its athletes were high on cocaine; many people say NBA's 14-year-old drug policy is so antiquated and ineffective that it protects players despite behavior that is illegal and commonplace; under collective bargaining agreement, league allows mandatory drug testing of rookies only, does not list marijuana as prohibited substance, and prevents teams from testing veterans for cocaine and heroin except under rare circumstances; photos (M)