When school started last fall at one of the nation’s most competitive and prestigious public high schools, the incoming freshman class looked different by design.

Compared with previous classes at Thomas Jefferson High School for Science and Technology in Alexandria, Va., there were more Black and Hispanic students, as well as white students — but fewer Asian students.

That is because standardized testing that had once been the key to admission was eliminated. Top students were admitted from a cross-section of schools, and weight was given to poorer students, as well as to students learning the English language.

Now, those policies are at the center of a federal lawsuit filed by an organization called Coalition for TJ, with the aid of the Pacific Legal Foundation, a conservative group that is taking on public high school admissions and has filed similar lawsuits in New York and Montgomery County, Md.

The organization argues that the school’s new admissions process was designed to racially balance the student body at the expense of Asian American students. The group is pushing for the school’s new process to be scrapped, saying that it discriminates along racial and ethnic lines.

If the lawsuit prevails, it could block future efforts at elite public high schools that are trying to diversify their students by race and income.

Wen Fa, a senior attorney with the Pacific Legal Foundation, said the changes made to the admissions criteria for the class of 2025 were merely proxies for race.

“They’ve completely revamped the admissions system, and they’re covertly doing that by the use of proxies,” Mr. Fa said.

Julie Moult, a spokeswoman for the school system, disagreed, saying the new admissions system was “merit based and race blind.” The race and ethnicity of applicants, largely drawn from the top 1.5 percent of each school, are unknown to the review panel, she said.

The decision, which could be issued sometime soon, will occur at an already volatile time for elite schools that are considering how to admit students. The Supreme Court is set to hear arguments on the question of whether Harvard and the University of North Carolina can consider race as a factor in admissions.

The case in Virginia, however, could break new ground. Unlike Harvard or the University of North Carolina, Thomas Jefferson never even mentions race as an admissions criteria; it instead uses other measures — like ZIP codes — to boost diversity.

Justin Driver, a Yale law professor, called the lawsuit aggressive because the plaintiffs were taking on a practice that no current Supreme Court justice had ever stated was a problem — the use of what school administrators say is race-neutral criteria to pick students.

The issue, he said, is “the next battle in the aftermath of a Supreme Court decision that would eliminate affirmative action.”

“These cases,” he continued, “are the next wave in this effort.”

Mr. Driver, author of a 2018 book on the Supreme Court and education, said Thomas Jefferson’s new policy shared similarities with the University of Texas plan that guarantees admission to the top students from each of the state’s high schools.

But the Pacific Legal Foundation and some parents say that the new admissions criteria is hardly race neutral, and that it deliberately targets Asian American students, many of whom score well on admissions tests.

Hemang Nagar, an Indian immigrant whose son was admitted to Thomas Jefferson in the class of 2025 despite the changes, is among the parents behind the lawsuit.

“This had nothing to do with the George Floyd murder, but that incident was used to push this down everybody’s throat,” Mr. Nagar said. “I think the case will go to the Supreme Court, and I think we will win.”

Asian Americans were the only racial group to see their numbers decrease under the new admissions system, to 54 percent from 73 percent.

The percentage of Black students increased to 7 percent from no more than 2 percent. Hispanic students increased to 11 percent from 3 percent. White students increased to 22 percent from 18 percent.

Overall in the Fairfax County school system, about 37 percent of students are white, 27 percent are Hispanic, 20 percent are Asian and 10 percent are Black.

Damilola Awofisayo, a senior who heads Thomas Jefferson’s Black Student Union, said she noticed an immediate change when the new class arrived.

“We have so much engagement and community,” said Damilola, 18, describing how the club’s previously sparse membership had grown. Its meetings now include vibrant discussions about current affairs through an African American lens.

As a freshman, she met students who seemed ignorant about Black people and made inappropriate comments. “My freshman year, I got comments that ‘You’re only at the school because of affirmative action,’” Damilola said, even though she had taken the same rigorous test as everyone else.

While she is reserving judgment on the new admissions system, she said that certain parts of it — including the geographic diversity requirement — were improvements. “It just makes things more equitable overall for everyone,” said Damilola, who is Nigerian American.

The Pacific Legal Foundation was founded in 1973, during Ronald Reagan’s tenure as California governor, by his supporters who envisioned a conservative version of the American Civil Liberties Union.

Since then, the organization, based in Sacramento, has expanded greatly. Its most recent annual budget was $17 million. Critics points to the group’s well-heeled donors and partners, including the Kochs, the Atlas Network and the Uihlein family, who operate the large business products supply company Uline, as proof that it is heavily influenced by business interests. The foundation says its support comes from 6,400 donors.

The foundation has a successful track record: 14 victories in Supreme Court cases. It is also known as a prolific filer of “friend of the court” briefs, including in support of Students for Fair Admissions, the Virginia-based group waging a legal battle against affirmative action at Harvard and North Carolina.

Mr. Driver, the Yale professor, noted that those cases pitted various ethnic groups against one another in ways that sowed division. At Thomas Jefferson, the controversy over class selection dates back decades, according to Jorge Torrico, a 1998 graduate.

When he attended, Mr. Torrico was an undocumented Bolivian immigrant who gained admission with the help of a foundation program that coached students through the application and testing. When he arrived, he said, “classmates immediately accused me of getting in through affirmative action.” He is now part of a group devoted to mentoring students to increase diversity at Thomas Jefferson.

In the early 2000s, the school ended an affirmative action program based on legal advice, according to Daniel A. Domenech, the former superintendent of Fairfax County schools.

His efforts to push through an alternate plan met political backlash, he said. And when he left the post in 2004 he felt a sense of frustration over that failure.

“This is a big issue in education right now,” said Dr. Domenech, currently executive director of the School Superintendents Association. “The whole issue of equity and lack of equity in our school systems is a glaring one.”

The controversy over Thomas Jefferson’s racial makeup flared once again in June 2020, when Black Lives Matter protests swept the country. The school’s principal, Ann Bonitatibus, wrote a soul-searching message to families. Why, she asked, did the school of about 1,800 students include only 32 Black students and 47 Hispanic students?

It was a call to action during a national period of racial reckoning, she said, urging families, “Please think of the privileges you hold that others may not.”

Spurred on by questions from the state’s education department about racial equity, as well as the concerns of other Democratic politicians, Thomas Jefferson revised its admissions policies.

Documents later released in court revealed that one school board member worried in a text that the new admissions policy had “an anti-Asian feel.”

Perhaps signaling the future of the lawsuit, the U.S. district judge presiding over the case, Claude M. Hilton, expressed skepticism about the school system’s claim that its revised admissions policy is race neutral.

“Everybody knows the policy is not race neutral, and that it’s designed to affect the racial composition of the school,” said Judge Hilton, a Reagan appointee. “You can say all sorts of good things while you’re doing others.”