The two bids will compete with a plan by MGM Resorts to operate Maryland’s sixth casino at National Harbor, the 300-acre mini-city on the Potomac River. The proposal to build that $800 million facility was submitted to the state Thursday.

A Maryland panel is expected to take several months to weigh the proposals and aims to choose one by the end of the year. The new casino could open by 2016.

Penn National said Friday that its vision for Rosecroft includes a casino with slot machines, table games and a poker room, accompanied by a hotel with a pool and spa, several eating establishments and an entertainment center. The company said it also plans to build a new grandstand at the horse track in Fort Washington.

Meanwhile, a newly formed subsidiary of Greenwood Racing filed a surprise bid to build a casino on a nearby 22-acre parcel at the intersection of Indian Head Highway and Old Fort Road. The company, which owns the Parx Casino north of Philadelphia, said it would offer many of the same amenities, including live entertainment and “best-in-class branded restaurants and bars and lounges.”

Las Vegas-based MGM has promised a “luxury resort” with a hotel, restaurants and retail, an entertainment venue, a spa and other attractions. The proposed MGM site is up a hill from the main National Harbor development.

The size of the gaming floors vary significantly in the proposals. Plans for the Parx call for 4,750 slot machines; MGM proposes 3,600. Penn is asking for only 500 machines for reasons company officials did not make immediately clear. All three venues would have between 140 and 170 table games, such as blackjack and roulette.

MGM’s bid had been anticipated for months. The company spent about $40 million last year promoting a ballot proposal to expand gambling in Maryland and to authorize a Prince George’s casino. (In addition to authorizing a sixth casino, the ballot measure voters approved in November allows table games, such as blackjack and roulette, at the state’s formerly slots-only venues.)

Penn National, which spent a similar amount trying to defeat the measure, remained coy about its intentions until Friday’s deadline. By midafternoon, Rosecroft’s Web site had been updated to include a rendering of Penn’s vision for a casino at the once-shuttered horse track.

Hollywood Casino is the most common brand name among the 22 casinos that Penn operates. A small casino that the Pennsylvania-based company owns in Perryville, in the northeastern corner of Maryland, carries the moniker, as does Penn’s highly lucrative property in Charles Town, W.Va.

Analysts said Penn’s opposition to last fall’s ballot measure in Maryland appeared motivated by a desire to protect its customer base in Charles Town against an MGM-run casino in Prince George’s.

Penn bought Rosecroft at a bankruptcy auction in 2011 with the hopes of putting a casino there, but the company’s calculations changed after Prince George’s County Executive Rushern L. Baker III (D) announced that National Harbor was his preferred site.

“We are looking forward to a fair and objective selection process and working with the local community and the state regulators to make this vision of a Rosecroft Raceway of the future a reality,” Tim Wilmott, president and chief operating officer of Penn National, said in a statement Friday.

The Prince George’s location has been coveted, in large part, because of its proximity to the nation’s capital and to Virginia, where casino-style gambling is illegal.

Under state law, the panel that will pick the winning bid must weigh a variety of criteria to determine which proposal is in the state’s best interests.

There are Maryland casinos operating in Anne Arundel, Worcester and Cecil counties. A fourth venue is scheduled to open this month in Allegany County, and a fifth casino is expected to debut in Baltimore next year.