Lawyers for Atlanta Public Schools have sent state investigators a defiant letter, ratcheting up the tension in an already-strained relationship.

In a three-page letter, sent Friday and obtained by The Atlanta Journal-Constitution, district officials denied obstructing the state’s criminal investigation into test-tampering, as investigators alleged last week. The letter objected to accusations that school officials have for years systematically retaliated against employees who reported cheating on state tests.

The school system also refused to cease its internal inquiry into allegations that a high-ranking district official allegedly advised a dozen principals to tell GBI agents to “go to hell.”

The letter could set the stage for further clashes this week with the three state investigators, who were appointed by former Gov. Sonny Perdue last year to find out whether widespread test-cheating took place in Atlanta schools.

“Notwithstanding the status of your investigation,” the district letter said, “APS has both the continuing authority and responsibility to investigate misconduct involving any of its employees.”

The state investigators have told the district not to investigate any cheating-related matters because doing so could interfere with the state’s investigative work.

The district’s sharp response capped a week in which two top officials faced scrutiny for disparaging the state investigation.

A story in The Atlanta Journal-Constitution last Sunday revealed the district was investigating whether Tamara Cotman, a regional superintendent supervising about 25 Atlanta schools, told a dozen principals not to cooperate with GBI agents looking into cheating. She allegedly asked the principals to pen memos telling the GBI to “go to hell,” then asked them to read the notes aloud.

The district reassigned Cotman on Monday. Her lawyer has denied that she broke any district policies or laws.

On Wednesday, Channel 2 Action News reported it had obtained a recording of a telephone conference call during which Superintendent Beverly Hall’s deputy, Kathy Augustine, called the state investigation “extremely denigrating,” “disrespectful” and “bizarre.”

The comments seemed to violate the spirit, if not the letter, of Hall’s earlier instructions to employees to cooperate fully with the state inquiry.

State investigators hit back Wednesday with a three-page letter that castigated the district for what it called “a pattern and practice of intimidating, threatening, and retaliating against teachers and other personnel who report cheating or who question the propriety of principals’ and test coordinators’ conduct in administering the CRCT [the state Criterion-Referenced Competency Test].”

The investigators — Mike Bowers, Bob Wilson and Richard Hyde — accused district administrators of suppressing a complaint about the Cotman meeting. The district’s decision to leave her in her post for two months before reassigning her, the investigators wrote, gave her time to retaliate against at least one subordinate.

“APS’ failure to at the very least notify us of this incident raises serious concerns as to APS’ attempts to protect those in its ranks who engage in intimidation of potential witnesses to cheating,” the investigators’ letter said.

The letter also ordered the district to cease investigations into test-tampering in 2010, saying such an examination would require the district to interview the same witnesses as state investigators. Doing so could intimidate educators and interfere with the state inquiry, the letter said.

The investigators demanded that the district promise in “clear and unequivocal writing” by Thursday to stop any investigations into CRCT-related matters.

In its response, the district denied that its look at suspicious erasures on the 2010 tests would involve interviewing the same witnesses. Hall has “made clear that APS is only conducting an analysis of the 2010 erasure data,” according to the district letter.

“Let me reaffirm on its behalf that APS will continue to cooperate with you in the special investigation, has not obstructed your investigation, and will not condone obstruction,” the letter said.

The district also asserted its right to investigate potential misconduct of employees such as Cotman, objecting to the investigators’ claim to be the “sole investigators” of such claims. Only the school system can discipline employees who violate its code of conduct, the letter said.

The letter defended the district’s hiring of an outside lawyer to investigate Cotman and denied she was reassigned because of the AJC’s story. But the letter did not address the investigators’ criticism that the district should have notified them of the allegations or that Cotman retaliated against a subordinate.

The letter denied that a pattern of witness intimidation exists. It called the investigators’ accusations “highly improper during a pending investigation.” The district said the allegation that it has protected those who engage in such intimidation “unwarranted, belied by APS’ swift action to investigate all allegations of possible misconduct.”

The district’s lawyers, Robert S. Highsmith Jr. and J. Tom Morgan, closed their letter by saying, “I trust this correspondence satisfies your inquiry.”

Reached Saturday, Mike Bowers, former Georgia attorney general and one of the special investigators, declined to comment.