Mitt Romney has proposed marriage rights for some gay and lesbian couples.

The 64-year-old Romney made his proposal during a wide-ranging interview with the Boston Herald's editorial board.

Romney proposed a federal constitutional amendment that would allow gay couples already legally married to remain married but bar future marriages of gay couples.

“I think it would keep intact those marriages which had occurred under the law but maintain future plans based on marriage being between a man and woman,” Romney told the paper.

The three-tier system is similar to what has already happened in California, where passage of a gay marriage ban, Proposition 8, put an end to the weddings of gay couples, but the state's highest court kept intact the marriages of 18,000 gay couples performed during the brief window when such unions were legal.

Romney's comments come just days after a gay Vietnam veteran asked him his thoughts on Republicans' plans to repeal a gay marriage law in New Hampshire. Romney said he supported the effort to repeal the law. In an interview with MSNBC's Chris Matthews, the veteran, Bob Garon, said Romney “doesn't know about the constitution.”

(Related: Mitt Romney inconsistent on gay rights? Depends on who you ask.)