One week after it reaffirmed a woman's basic right to abortion, the Supreme Court yesterday effectively made it easier for states to impose waiting periods and other restrictions on women who want to end their pregnancies.

The court's one-sentence order denying review of a Mississippi case set back abortion rights activists, who will now have more difficulty challenging state abortion restrictions. It also opens the door for a new era of litigation as the courts define when a woman faces an "undue burden" -- the court's new legal standard -- in trying to obtain an abortion.

Equally important, yesterday's order implies that once an abortion restriction is upheld in one state, other states may implement it unless individual cases can be made that it infringes on a right to abortion. Some constitutional experts say this signals a change because most abortion laws since 1973 came to the Supreme Court under general challenges soon after they were enacted.

Instead of fighting an abortion law when it is passed, women would have to submit to state regulations and challenge laws only after gathering evidence of their potential infringement on the right to abortion, according to abortion rights activists.

In yesterday's dispute, the court let stand a Mississippi requirement that women seeking abortions in one of the state's three clinics first be told about maternal health risks and fetal development, then wait 24 hours.

Mississippi officials argued that the required abortion counseling and waiting period are necessary so that women are able to fully understand the medical risks of abortion, compared with childbirth, and to know the age of the fetus.

But the physicians who challenged the law contended that the requirement was too onerous for poor women who must travel long distances to abortion clinics. The effect of yesterday's order "is women who saved up their nickles and dimes, saved up their sick days, will have to go twice {to a clinic} or stay overnight," said Rachael N. Pine, a lawyer with the Center for Reproductive Law & Policy in New York, who represented three Mississippi doctors who challenged the law.

The Mississippi waiting period, which took effect last August, is comparable to a Pennsylvania law upheld last June.

Yesterday's court order followed by one week a court decision not to revive a ban on abortions in the territory of Guam. That order effectively affirmed earlier rulings that abortion is a constitutional right and sent a message that abortion prohibitions will not stand.

The remaining, overriding question is how far states may go in regulating an abortion right and how much they ultimately may infringe on Roe v. Wade, the 1973 landmark ruling that made abortion legal nationwide.

Yesterday's order, far from the last word on the issue, appears to indicate that not only will states have an easier time adopting regulations than they did under the Roe standards, but also that it would be easier than was first thought when the court issued its new abortion guidance in last June's Planned Parenthood of Southeastern Pennsylvania v. Casey.

The order in Barnes v. Moore also shows that the coalition of Justices Sandra Day O'Connor, Anthony M. Kennedy and David H. Souter, which effectively blocked the court last term from reversing abortion rights, cannot always be relied on to rescue the interests of abortion activists.

"If women across the nation are counting on O'Connor, Kennedy and Souter always agreeing, then we have nothing," said Pine.

T. Hunt Cole Jr., special assistant attorney general in Mississippi, said that if the court had taken the case, and allowed Mississippians to challenge a law that had been upheld in Pennsylvania, the end result could be different standards among the states.

The "undue burden" test of last term's Casey requires a less scrutinizing look at a state law than Roe v. Wade dictated.

But how much lower is still uncertain. The court said an undue burden is one that "has the purpose or effect of placing a substantial obstacle in the path of a woman seeking an abortion" of a fetus that is not yet viable to live outside the womb.

In the Mississippi case, the 5th U.S. Circuit Court of Appeals said that because the physicians were challenging the general validity of the Mississippi act, rather than how it had been applied to a particular party, they "must establish that no set of circumstances exist under which the act would be valid."

"In light of Casey's holding substantially identical provisions of the Pennsylvania act facially constitutional, the plaintiffs cannot satisfy this 'heavy burden,' " the appeals court said.

The appeals judges noted that the physicians had wanted to make a case for a waiting period being more burdensome in Mississippi than in Pennsylvania and that the Casey ruling had made numerous references to the findings of fact in Pennsylvania.

But, at bottom, the appeals court said that the unusual joint opinion in Casey, written by O'Connor, Kennedy and Souter, intended to establish a standard of general application.