The Manhattan district attorney’s office suggested on Monday that it had been investigating President Trump and his company for possible bank and insurance fraud, a significantly broader inquiry than the prosecutors have acknowledged in the past.

The suggestion by the office of the district attorney, Cyrus R. Vance Jr., came in a new federal court filing arguing that Mr. Trump’s accountants should have to comply with a grand jury subpoena seeking eight years of his personal and corporate tax returns. Mr. Trump has asked a judge to declare the subpoena invalid.