A day before he announced that only four kids in NYCHA housing tested positive for elevated lead levels, Mayor Bill de Blasio was briefed privately that the number was actually 202, emails obtained by The Post reveal.

Between 2014 and 2016, “four children in NYCHA tested positive for elevated lead levels and they were in NYCHA apartments where physical fixes had to be achieved,” de Blasio said in a press conference on Nov. 20 in his first public assessment of the extent of the crisis at the New York City Housing Authority.

“Four kids is the universe, two of them specifically about paint, and thank God no lasting health impact that we can find at this point,” he added.

But the mayor had received a four-page briefing paper a day earlier alerting him to the higher number of affected children.

“6,881 tested positive for elevated lead blood levels” between 2010 and 2015, said the document sent by top City Hall aide Wiley Norvell on Nov. 19. “Of those, 202 children lived in NYCHA developments across 133 apartments.”

Critics accused de Blasio of using data from a shorter time span in order to announce a smaller number of affected kids.

“It’s the latest confirmation of what we’ve long known, that City Hall has systematically misled the public and public officials about the true extent of lead poisoning in public housing,” said Councilman Ritchie Torres (D-Bronx), who chairs the City Council’s investigations committee and previously oversaw public housing.

“The claim that there were only a few cases of lead poisoning in public housing have been proven a lie with these emails.”

But City Hall spokeswoman Olivia Lapeyrolerie said de Blasio gave an accurate “caveat” to the number when he provided it to the public at the press conference.

Lapeyrolerie also said the administration has taken steps to strengthen the city’s lead policies in recent months.

“We’ve reduced childhood lead exposure by 90 percent, but we refuse to rest there,” she said.

Additionally, the thousands of pages of heavily redacted documents obtained under the Freedom of Information Law show members of de Blasio’s administration had been aware of the tally for more than a year — and less than two months after being notified of potential lead problems at NYCHA.

The first inklings of the crisis arose in late March 2016, when federal prosecutors in Manhattan went to court to demand documents from the authority.

In April, then-NYCHA Chairwoman Shola Olatoye first informed Deputy Mayor Alicia Glen that the authority had failed to conduct lead inspections required by the feds and city law since 2012 — and that it had covered up the lapses.

The emails obtained by The Post show NYCHA officials briefed the top levels at City Hall as early as May 2016 that, between 2010 and 2015, 202 children who lived in the city’s public housing tested positive for lead levels that the city Health Department considered dangerous.