On a fall afternoon in 2002, the New York City police broke up a protest in front of Gov. George E. Pataki’s office in Midtown Manhattan and hauled a dozen demonstrators away.

The protesters were demanding that Mr. Pataki repeal the state’s 30-year-old drug sentencing laws, widely regarded as the nation’s most unforgiving. One of those placed in plastic handcuffs and carted off to a police station was a state senator named David A. Paterson.

Now, with Mr. Paterson in the governor’s mansion and Democrats in control of both houses of the State Legislature, an aggressive effort is under way to finally dismantle what remains of the stringent 1970s-era drug laws, which imposed stiff mandatory sentences as a way to combat the heroin epidemic then gripping New York City.

The Assembly is expected to pass legislation on Tuesday that would once again give judges the discretion to send those found guilty of having smaller amounts of illegal drugs to substance-abuse treatment instead of prison and allow thousands of inmates convicted of nonviolent drug offenses to apply to have their sentences reduced or commuted.