Maryland plans to invite bids next week from companies interested in operating a Prince George’s County casino, the next step in a contentious process to bring Las Vegas-style gambling to the doorstep of the nation’s capital.

The approval by a state panel Thursday of a “request for proposals” came less than three months after voters approved Question 7, a measure that authorizes a sixth Maryland casino and allows previously designated slots locations to add table games, such as blackjack and roulette.

The 104-page document allows bids to operate a casino in a pre-determined swath of Prince George’s that includes both National Harbor, the 300-acre mini-city on the Potomac River; and Rosecroft Raceway, the horse track in Fort Washington that reopened in 2011.

MGM Resorts, which spent $40 million urging voters to pass Question 7, said Thursday that its interest in building a “destination resort” at National Harbor is “unabated” and pledged to put in a bid before the May 10 deadline.

“We’ve been studying the market for months, drawing up designs and programming for a resort that will be unique to this location, its history and community,” MGM spokesman Gordon Absher said. “We plan to earn the privilege of being Maryland’s newest license holder.”

Karen Bailey, a spokeswoman with Penn National, a national gambling behemoth that owns Rosecroft, said her company is considering whether to bid, despite spending $40 million trying to persuade voters to defeat the ballot measure.

Donald C. Fry, chairman of the panel that picks casino locations, said he hopes to name a winning bidder by the end of the year, following extensive background checks of the companies that apply. The earliest a Prince George’s location is likely to open is 2016.

“I would think it’s probable, from everything we hear publicly, that there will be multiple bids,” Fry said.

Senate President Thomas V. Mike Miller Jr. (D-Calvert), among the biggest gambling boosters in the legislature, predicted the award of a license would ultimately be decided in the courtroom, given the record spending by MGM and Penn National on the ballot measure and the hostility between the companies.

“It’s going to wind up in litigation, no matter what,” Miller said. Nonetheless, he said, the economic potential for a casino that would draw heavily from the District and Northern Virginia is enormous.

With the approval of Question 7, the Baltimore-Washington corridor is well on its way to becoming one of the most concentrated casino markets outside Las Vegas.

The state’s largest casino, Maryland Live! in Anne Arundel County, opened in June. And Caesars Entertainment plans to open a Horseshoe-brand casino in Baltimore next year. Three smaller facilities are open or will open in less-populated parts of the state.

Modeled upon legislation that the General Assembly passed in August, the request for proposals approved Thursday would allow a casino to be within four miles of the intersection of Bock and St. Barnabas roads.

It’s possible that bids could emerge for locations other than National Harbor or Rosecroft, though no one has publicly disclosed such plans.

For months, rumors have ebbed and flowed about the possible interest of another gambling company, Wynn Resorts. But Michael Weaver, the company’s senior vice president of marketing, said this week that it has no plans to submit a bid.

MGM has promised an $800 million complex with a hotel, high-end restaurants and retail, an entertainment venue, a spa and other attractions.

Penn National has said less about what it envisions at Rosecroft.

For much of the fall, a barrage of TV ads funded by Penn National argued that politicians who supported the expansion plan were peddling false promises about education funding and that the plan was too generous to “casino special interests.”

Analysts said Penn was motivated by a desire to protect a casino it owns in Charles Town, W.Va., that stands to take a hit from a Prince George’s location.

Penn National, which operates 29 casinos and racetracks, bought Rosecroft, the once-storied harness racing track in Fort Washington, at a bankruptcy auction with the aim of building a casino on the property.

Those plans were dealt a blow last year when Prince George’s County Executive Rushern L. Baker III (D) endorsed National Harbor as his preferred location. The developer of National Harbor subsequently announced MGM as its chosen operator.