This week's ruling on pay discrimination is a supremely enlightening example of the arbitrariness of the law and the difference one justice can make.

Beyond that, it reifies the concept of the Supreme Court as a lagging indicator of American politics.

It is the latest example of what is destined to become a string of famously narrow 5-4 Roberts Court rulings. The Supreme Court decided to turn down a female worker's lawsuit against an employer who underpaid her compared with her male co-workers.

Lilly Ledbetter was an area manager in Goodyear's Gadsen, Ala., plant for almost two decades starting in 1979.

According to dissenting Justice Ruth Bader Ginsburg, Ledbetter began her career with earnings comparable to that of her male colleagues. By the time she retired, her $3,700-per-month payment was some $550 lower than the least-well-paid similarly situated man and $1,550 less than the best-paid male area manager. These disparities reduced her retirement benefits.

The majority opinion in the case, written by newcomer and President Bush appointee Samuel Alito, reasons Ledbetter lost her right to sue for sex discrimination because Title VII requires all claims be filed within 180 days of the discriminatory act. Ledbetter didn't file her claim until a few months before her retirement, years after her salary dwindled compared with male colleagues.

The majority could have just as easily reasoned the 180-day time limit, written into law by Congress, should apply only once the person "knows or should have known of" the discrimination a rule that is often applied to other laws. Or, as Justice Ginsburg writes, the 180-day limit should be imposed against single discriminatory acts such as hirings, firings and promotions, not in cases that build up slowly over time. Ledbetter didn't find out about her lower pay until just before she retired. Goodyear took steps (as most employers do) to keep pay disparities secret.

The majority's decision to rule as it did was the height of arbitrariness. The law is replete with examples of judges applying "equitable tolling" or "equitable estoppel" to push back deadlines that simply don't make sense given the facts of a particular case. Justice Alito could easily have chosen to do so in Ledbetter's case.

Had retired Justice Sandra Day O'Connor still been on the bench, odds are she would have sided with the dissent. Thus, the difference one justice can make.

Justice Alito was also nominated to the court by a president whose conservative popularity has been similarly battered as the public gets a closer view of the impact of conservative governance (or Bush's brand of it) on this nation. The public is clearly tiring of his arch-conservative politics, and by inference, Alito's as well. Thus, Alito's judicial perspective is a remnant of the political past.

Alito's methodology, beginning as a Reagan Justice Department appointee, was not to repeal civil rights legislation outright just to gut it by making it impossible to enforce in ways that don't attract much public attention.

Unfortunately, Ledbetter makes clear this type of judicial reasoning is a beacon for what is to come from the Roberts court on the civil rights front.

Bonnie Erbe is a TV host and writes for Scripps Howard News Service. Her e-mail address is bonnieerbe@CompuServe.com.