The NCAA’s investigation of former St. John’s center Abe Keita’s allegation that he received regular monthly payments of $300 from a senior member of the basketball staff has focused on a loan Keita obtained as a freshman when he was a partial qualifier, The Post has learned.

Because Keita, a native of Ivory Coast and not a U.S. resident, was not eligible for an NCAA Pell Grant, which is supposed to cover a student-athlete’s living expenses, Keita, received a need-based financial aid loan from St. John’s.

The loan was to be paid back according to whatever terms were stipulated at the time of the signing. Once Keita became academically eligible, he began receiving a monthly room stipend. Sources said that Keita was making the payments on the loan but a senior member of the basketball staff allegedly was funneling cash back to Keita.

The arrangement of such a loan is not common, but it does not violate NCAA rules. St. John’s consulted the Big East Conference on filling out the paper work for the loan.

But if a senior member of the basketball staff were reimbursing Keita, it was an NCAA violation. The investigation is not likely to end any time soon as the NCAA seeks to interview all the parties involved.

Sources familiar with NCAA procedures said, if the allegations are true, St. John’s probably would have to forfeit one or more scholarships and could be placed on probation. Television appearances and post-season play probably would not be affected.

As reported exclusively in yesterday’s Post, NCAA representatives were at St. John’s yesterday. It was unclear if this were a preliminary investigation or if the university had received a more formal letter of inquiry.

St. John’s has consulted with the Kansas-based law firm of Bond, Schoeneck & King, which specializes in NCAA matters. It was unclear if St. John’s had retained the elite firm, but it would wise to do so.

Because of its familiarity with the NCAA, Bond, Schoeneck & King often conducts its own internal investigation and then recommends penalties to the NCAA, that usually are deemed acceptable.

St. John’s worked with the firm in 2000 when former point guard Erick Barkley was under investigation for trading cars with a longtime family friend. St. John’s was not placed on probation.

Sources told The Post that the NCAA probably would want to speak with former St. John’s athletic director Ed Manetta, current AD David Wegrzyn, former coach Mike Jarvis, Keita and current and former players.

“All I can say is what I’ve said in the past,” said Jarvis. “We did our best to supply Abe Keita with a quality education.”

Working in St. John’s favor is the fact that Jarvis already has been fired, Alex Evans, the director of basketball operations resigned last week to take a job in the private sector and St. John’s self-reported the possible repayment violation.