The Supreme Court today loosened the restrictions on what companies and unions can spend on television advertisements just before elections, and in so doing may well have affected the thinking of political strategists for the 2008 elections.

By 5 to 4, the court ruled that an anti-abortion group in Wisconsin should have been allowed to broadcast ads before the 2004 race for the United States Senate in that state. In its ruling today, the high court opened a significant loophole in the Bipartisan Campaign Reform Act of 2002, familiarly known as the McCain-Feingold law, to curb donations to campaigns.

Writing for the majority, Chief Justice John G. Roberts Jr. said that, when regulating what can be said in a campaign and when it may be said, “the First Amendment requires us to err on the side of protecting political speech rather than suppressing it.”

In another 5-to-4 ruling involving free speech, the court ruled today against an Alaska high school student, finding that educators can prohibit student expression that can be interpreted as advocating drug use.

Today’s ruling in the campaign-finance case focused on the Supreme Court’s decision in 2003, when there was a different lineup of justices, upholding a key section of the McCain-Feingold law. That section bars companies and unions from paying for ads even mentioning the name of a candidate for federal office in the 60 days before a general election or the 30 days before a primary.

The 2004 ads in question mentioned Senators Russell D. Feingold and Herb Kohl, both Wisconsin Democrats, and urged viewers to contact them and urge them to oppose their Democratic colleagues’ opposition to some of President Bush’s judicial nominees. The ads directed viewers to a Web site critical of Mr. Feingold, who was up for re-election.

Mr. Feingold and Senator John McCain, Republican of Arizona, were the main sponsors of the campaign finance law. Its supporters see it as a valiant attempt to regulate the spigots that pour oceans of corrupting money into political campaigns. Its detractors see it as interference with free speech, and as unrealistic in view of the huge sums of money needed to run a political campaign.

The Wisconsin Right to Life organization sued the Federal Election Commission, seeking a judgment declaring that the pertinent McCain-Feingold section was unconstitutional. A special three-judge federal court panel ruled in favor of the anti-abortion group, finding that the ads’ text and images did not show that they were “intended to influence the voters’ decisions” but were “genuine issue ads” that the government could not keep off the air.

Today, the Supreme Court majority concluded that the special judicial panel was right in holding that the ads should have been allowed. “Because WRTL’s ads may reasonably be interpreted as something other than an appeal to vote for or against a specific candidate, they are not the functional equivalent of express advocacy,” the majority said, using the term for ads that urge a candidate’s election or defeat.

To safeguard freedom of speech, the majority said, scrutiny of challenges to the McCain-Feingold law “must be objective, focusing on the communication’s substance rather than on amorphous considerations of intent and effect.”

In defining what qualifies as “express advocacy,” or ads zeroing in on a candidate to promote or denounce him, “the court should give the benefit of the doubt to speech, not censorship,” the majority said.

Chief Justice Roberts wrote the opinion upholding the special court. Siding with him were Justices Samuel A. Alito Jr., Antonin Scalia, Anthony M. Kennedy and Clarence Thomas, although the last three jurists would have gone further and declared the pertinent section of the law unconstitutional. Chief Justice Roberts and Justice Alito said only that the anti-abortion group’s ads should not have been banned under the section.

When the McCain-Feingold law was upheld in 2003, Chief Justice William H. Rehnquist was one of the four dissenters who would have overturned it. Justice Sandra Day O’Connor, who was succeeded by Justice Alito, wrote the majority opinion.

In the case decided today, Federal Election Commission v. Wisconsin Right to Life, No. 06-969, Justice David H. Souter wrote a dissent that Justices John Paul Stevens Ruth Bader Ginsburg and Stephen G. Breyer joined.

“After today,” the dissenters said, “the ban on contributions by corporations and unions and the limitation on their corrosive spending when they enter the political arena are open to easy circumvention, and the possibilities for regulating corporate and union campaign money are unclear.”

The dissenters expressed dismay over today’s ruling and said it could portend a new wave of public cynicism about the role of big money in politics.When the case decided today was argued on April 25, Solicitor General Paul D. Clement, arguing on behald of the election commission, said that to find that the Wisconsin ads should have been allowed to run would leave the McCain-Feingold law “wide open.” Justice Breyer predicted then that a ruling like today’s could mean, in effect, “Goodbye, McCain-Feingold.”

Whether that is indeed true may not be clear for a while. But it seemed abundantly clear after today’s ruling that the broader debate over campaign money, which a California politician once famously called “the mother’s milk of politics,” will go on, especially with the 2008 presidential campaign already well under way.

Senator Feingold issued a statement today expressing disappointment. “The Federal Election Commission should not allow today’s decision to open the door for a return to the pre-McCain-Feingold days of phony issue ads and unlimited corporate and union spending on campaigns,” he said. “If that is the result, the court will have done the country a great disservice.”

In the Alaska case involving free speech, the court found that a high school principal and school board did not violate a student’s rights by punishing him for displaying the words “Bong Hits 4 Jesus” on a banner across the street from the school as the 2002 Olympic torch parade went by.

When the case was argued on March 19, Kenneth W. Starr argued — successfully, as it turned out — on behalf of the school authorities that, whatever rights students may have to express themselves, thumbing their noses at school officials’ anti-drug messages is not one of them.