The Bush administration went to the Supreme Court yesterday to defend a flag-burning law it doesn't like as a matter of law or politics.

The Flag Protection Act of 1989 was passed by Congress in response to the court's ruling last summer striking down a Texas law. President Bush had called instead for a constitutional amendment to prohibit flag burning, saying it was the only way to stop the "egregious offense" of desecrating the American flag.

But Congress disagreed, and while Bush expressed his "serious doubts that it can withstand Supreme Court review," he allowed the measure to become law without his signature.

Now, the inevitable flag burnings have produced the inevitable constitutional challenges, and the issue is once again before the Supreme Court.

The new law was designed to avoid the constitutional pitfall of the Texas statute, and of the previous federal law, which made it a crime to knowingly "cast contempt" on the American flag. In contrast, the new statute purports to be "content-neutral," promoting the government's interest in protecting the "physical integrity" of the flag by simply prohibiting any burning or other destruction, no matter what the motivation.

However, two federal district court judges -- one here and another in Seattle -- have struck down the law as an infringement on freedom of speech. Under the law's provisions, the cases go directly to the Supreme Court, and the Bush administration now finds itself in the tricky position of defending a law it has already announced is unconstitutional.

As a legal matter, the administration is duty-bound to defend the law in court so long as there are reasonable grounds for doing so, yet a ruling striking down the law would prove the administration was right originally when it warned that no statute would pass constitutional muster.

As a political matter, having the law overturned would spark a renewed push for a constitutional amendment -- a welcome diversion for Republicans from the troublesome issue of abortion rights, particularly if it comes before the 1990 elections.

If the court declares the law unconstitutional, as many observers expect, "flag politics" will become "an issue in every state legislative election in 1990," said Duke University law professor Walter Dellinger, who testified before Congress in opposition to a constitutional amendment.

Although new cases taken at this stage of the Supreme Court term would normally be heard next fall, the statute provides that challenges to the law be expedited "to the greatest extent possible." The administration asked the justices to speed up the normal briefing schedule and hear the case April 25.

In last term's case, the justices, splitting 5 to 4, overturned a flag-burning conviction under a Texas law that prohibited defacing or damaging the flag in a way that the person knows will "seriously offend" people.

Justice William J. Brennan Jr. said the law violated the First Amendment because it was designed to suppress speech -- and flag burning was deemed to be symbolic speech in this case.

"If there is a bedrock principle underlying the First Amendment, it is that the government may not prohibit the expression of an idea simply because society finds the idea itself offensive or disagreeable," Brennan said.

Opponents of the new law contended that it could not be considered "content-neutral" because the government would still be seeking to protect the flag because it is a national symbol -- a goal inherently related to expression.

"The reason we're going through this is to get to the people who really engage in contemptuous conduct toward the flag," Assistant Attorney General William P. Barr told the Senate Judiciary Committee in August. "And the only way that can be done . . .is through a constitutional amendment."

The two federal courts that have so far reviewed the statute have agreed wtih Barr that -- no matter what its phrasing -- its purpose is to restrict speech.

In the lower courts, the Justice Department, which prosecuted both cases, defended the law even as it said Barr's testimony continued to represent the Justice Department's views.

In the briefs filed yesterday, however, Solicitor General Kenneth W. Starr referred to the department's previous legal interpretation only in a footnote. Starr argued instead that flag burning, like obscenity, "fighting words," and libelous statements, "falls outside the scope of protected speech under the First Amendment."

Although the majority rejected that argument last term, Starr said, "this case presents the court with the opportunity to reconsider that premise" now that "the people's elected representatives -- the Congress and the president -- have made the considered decision that the physical destruction of the flag is -- uniquely -- anathema to the nation's values."

Not all legal observers agree that the administration was obligated to argue in support of the law.

"The executive is responsible for formulating his own constitutional views and . . . when the executive decides in his best judgment and after . . . appropriate deference to Congress that this one just ain't gonna wash," then it should let Congress defend the law, said former assistant attorney general Charles J. Cooper, who testified in favor of a constitutional amendment.

But the more traditional view, expressed by former deputy solicitor general Kenneth Geller, is that the executive branch has "a duty to take care that the law be faithfully executed. That involves defending acts of Congress when they're attacked in court unless the powers of the president are themselves implicated."

But the administration doesn't appear exactly confident of a Supreme Court victory. "We've always believed that a constitutional amendment was the correct approach to protecting the flag," White House spokesman Marlin Fitzwater said last week, "and have always believed that it would ultimately be necessary."