A former admissions director at Riverdale Country School has sued the elite institution, claiming it concealed a lack of commitment to diversity with a “window dressing” policy aimed at recruiting “full-paying Asians and non-Jews.”

In an unusual lawsuit, an English teacher, Shereem Herndon-Brown, claims that the school hired him as director of admissions to increase diversity among the student body but reneged on its contract with him when it failed to offer enough financial aid to the scholarship students he admitted.

Mr. Herndon-Brown said that when he gave up teaching English at Riverdale for an admissions job there, he had been led to believe that the school would support his efforts to increase racial and socioeconomic diversity at Riverdale.

Located in a leafy corner of the Bronx, Riverdale is one of the city’s most elite private schools. The school charges a tuition of $31,200, making it one of the most expensive day educations that New Yorkers can purchase for their children.

At the center of Mr. Herndon-Brown’s lawsuit against the school are two misfortunes unrelated to the admissions office. In July 2005, a large tree fell onto the on-campus home that Mr. Herndon-Brown was living in, he said in an interview. The temporary housing that the school then provided had a high lead content, leading to the poisoning of Mr. Herndon-Brown’s infant son, who suffered a fractured leg when the tree fell, the lawsuit alleges.

His son, now 2, will need to be monitored throughout young adulthood to track any effects due to the exposure to lead, Mr. Herndon-Brown said.

A legal complaint alleges that Mr. Herndon-Brown’s “dream job” of increasing diversity “turned into a young family’s worst nightmare as the school callously turned away qualified minority applicants, flouted the law by allowing a baby to occupy an apartment contaminated with lead,” and “failed to prevent a large crumbling tree from violently uprooting and crashing down on the house.”

Mr. Herndon-Brown’s lawyer, Edward Hayes, said the claims about Riverdale’s admission procedure are “semi-central” to the lawsuit. He said the legal complaint would be filed in state Supreme Court in the Bronx today.

Mr. Herndon-Brown, 32, said that when he was promoted in 2005 to the $90,000 a year admissions job, he was given a mandate to increase the school’s economic, ethnic, and religious diversity.

But Mr. Herndon-Brown alleges that the headmaster, John Johnson, later refused to provide enough financial aid to allow the students he recruited to attend Riverdale.

To stay within the financial aid budget and increase the diversity statistics, the legal complaint alleges that Mr. Johnson told his new admission officer to recruit “full-paying Asians” whose parents were wealthy enough to afford the tuition.

But Mr. Herndon-Brown claims that Mr. Johnson also told him not to recruit children of celebrity blacks. The complaint alleges that the two administrators spoke of a rival school, Horace Mann, where rap artist Sean “Diddy” Combs and filmmaker Spike Lee send their children, according to the lawsuit.

“Johnson opined that certain celebrity African-American parents would not be a good addition to the parent body,” according to the complaint.

Mr. Herndon-Brown also said he was instructed to recruit non-Jewish students.

When Mr. Herndon-Brown began placing students of color and non-Jewish students at the top of the financial aid list, he learned that there was not enough money to make competitive offers to top students, the lawsuit alleges.

Mr. Herndon-Brown, who is black, claims that the school’s decision to hire him amounted to “window dressing.”

School administrators countered claims yesterday that Riverdale was not committed to diversity.

The school headmaster, John Johnson, told The New York Sun that the school aggressively recruited minority students and that about 15% of the money it received in tuition went to financial aid.

Of Riverdale’s 1,050 students, about 20% are non-white, the principal of the upper school at Riverdale, Kent Kildahl, said. The school’s financial aid budget of $3.3 million a year goes to help pay the tuition of about 20% of the students, Mr. Kildahl, said in an interview yesterday.

“We think that with any objective observer our position would stand up and that these charges are simply not true,” Mr. Johnson said.

He said yesterday that the administration had asked Mr. Herndon-Brown “to try to increase diversity and in our case that would include more Asian students and it would also include more Hispanic and more African-American students and so forth.”

Mr. Johnson said that Mr. Herndon-Brown has “at best” mischaracterized his past conversations with him.

Mr. Herndon-Brown had been a rising star among school administrators and his decision to resign earlier this year and sue the school had come as a disappointment to them, Mr. Johnson said.

“The mystery is that we all quite liked him and respected him and did everything we could to support him,” the headmaster of the school said.