Maryland Senate President Thomas V. Mike Miller Jr. said Thursday that the General Assembly will not consider legislation this year to legalize sports gambling, meaning that the earliest the state could implement a system to authorize and tax betting on athletic contests is likely 2021.

“Sports betting is going to have to wait until next year,” Miller (D-Calvert) said Thursday when asked if lawmakers would consider legislation before the General Assembly adjourns early next month.

Miller, Gov. Larry Hogan (R) and House Speaker Michael E. Busch (D-Anne Arundel) had all expressed support late last year for legislation to approve sports betting, so that Maryland would not lag behind other states who are legalizing the practice.

But Miller said Thursday that the office of Attorney General Brian K. Frosh (D) told legislative leaders that the only way for Maryland to expand gambling is to amend the state constitution, which requires a public referendum.

Because there are no statewide elections in Maryland this year, the earliest that could happen is 2020. The Senate president said this year that all referendums should be approved in the General Assembly the same year they would go on the ballot.

Last spring, the U.S. Supreme Court lifted a ban that kept states, with the exception of Nevada, from allowing sports betting. In addition to the District, New Jersey, Delaware, Rhode Island, Pennsylvania, Mississippi, West Virginia and New Mexico have since legalized sports betting.

“Everybody’s got a head start: Las Vegas, New Jersey . . . it’s very unfortunate,” Miller said.