The mortgage bill is coming due for Standard & Poor’s.

The ratings agency, which allegedly fattened its bottom line during the housing boom by inflating the creditworthiness of residential mortgage bonds, could soon agree to pay $1.5 billion to US authorities to settle lawsuits in the matter, according to a report on Tuesday.

Talks between S&P and the Justice Department over the February 2013 lawsuit are ongoing and a settlement could be announced later this month, Reuters reported.

At the same time, S&P is expected to be banned from rating certain types of loans for commercial properties — its most lucrative line of business — a second report maintained.

The yearlong suspension — as part of the settlement of a second lawsuit, this one with the Securities and Exchange Commission — will bar S&P from the $550 billion commercial mortgage-backed securities, or CMBS, market.

It is expected to be unveiled as soon as Wednesday — and would constitute the most severe punitive action taken against the ratings giant since the 2008 housing bubble burst.

S&P was one of the companies that fueled the 2008 financial crisis by turning a blind eye to the risks in the subprime mortgages that Wall Street firms repackaged and sold to investors, it is alleged.

The company makes money by evaluating how likely investors are to get paid back if they buy certain kinds of debt. They then rate it from the highest “AAA” grade to a “D” for debt that is in default.

The attorneys general for New York and Massachusetts have also been investigating the alleged fixing, according to regulatory documents.

The agreement would be about three and a half years after the ratings agency downgraded the creditworthiness of the US government — a move that sent shock waves through the stock markets and pushed up the value of US debt.

The SEC sent the ratings agency a Wells Notice in July, saying that it was investigating the company for its CMBS ratings practices, according to regulatory findings.

Shares of McGraw Hill, S&P’s parent company, ended the day slightly higher at $90.96 in the wake of the news.

Catherine Mathis, a spokeswoman McGraw Hill, declined to comment on the settlement.