But even if such challenges succeed, they are unlikely to achieve many meaningful results, legal experts say. That is because judges seldom go a step further and actually order a state legislature to spend more.
"A court can find that a state government or a local government has violated its own laws with regard to protecting the poor," said Liz Krueger of New York's Community Food Resource Center. "But it rarely orders a legislature to change how it spends its revenue."
Yet many advocates for the poor, as they consider or prepare lawsuits, are zeroing in on state laws that obligate governments to care for the poor. Twenty-two states have such laws, often in broadly worded language.
As the federal government turns welfare spending authority and program design over to states, those laws have become vitally important for advocates seeking to restore aid.
The California lawsuit filed Tuesday, for example, argues in part that a threatened end to prenatal care for illegal immigrant women would violate a California state law requiring "medically necessary pregnancy-related services," regardless of immigrant status.
The stakes are especially high because the new federal law gives states the option of shaving $40 billion from public assistance programs in addition to the $54 billion reduction the federal government plans over the next seven years.
But those who have sued governments say taking on a government can be a long, frustrating battle full of illusory triumphs.
As an example, Krueger cited a string of court rulings over the past 10 years holding New York City in contempt for failing to provide enough homeless shelters.
"New York has been beaten up in court for the past 10 years," she said. "Have we assured the right to shelter? No."
Even when judges declare a city or state in violation of laws, they often leave it to the municipality to correct the problem, noted Steven Banks, a lawyer who represents the homeless for New York City's Legal Aid Society.
Only if that doesn't happen is a judge likely to order some specific remedy - for example, more money for homeless shelters or feeding programs.
And governments often appeal those rulings, meaning the entire process can take years.
"It's possible to make a difference in the long run," Banks said. "In the short run, it's very slow going in most state court systems."
In the District of Columbia, for example, advocates have long battled the city over its foster care program.
A federal judge first ruled against the city in 1991, ordering sweeping changes in indigent care.
Despite increasingly harsh edicts from the bench, little changed until 1995, when a court-appointed receiver began making some progress, said Tom Wells, director of the Consortium for Child Welfare.
Advocates for the poor are aware of such cases, and often plan to hedge their bets by arguing on many fronts.
In the California lawsuit, the ACLU argued on two fronts: that cutting off prenatal care violates state law and that it violates a 1994 federal court order blocking Proposition 187, which denied medical benefits to illegal immigrants.
A spokesperson for Gov. Pete Wilson, defending the plans, noted that Congress had approved the welfare changes and that President Clinton had signed them into law.
Some welfare rights groups have pointed to the opportunity of having, potentially, 50 different state laws to attack, instead of one federal standard. that would yield an all-or-nothing legal outcome.
But others caution that battling so many different governments could be far harder.