After investing five years and $50 million in an attempt to bring an NFL team back to Los Angeles, AEG is abandoning plans for its Farmers Field football stadium downtown.  The sports and entertainment conglomerate is no longer in discussions with the NFL or any teams about the project, company officials said Monday.

“I think it’s fair to say we have turned our attention to proceeding with an alternative development,” AEG Vice Chairman Ted Fikre said.

Fikre said AEG will not seek an extension of its deal with the city, which expires April 17 and hinges on a long-term agreement with a team. The city, which owns the proposed stadium land, had already given the company an additional six months.

AEG failed to attract an NFL team, even though many league owners and executives viewed the site favorably. In recent weeks, competing stadium proposals in Inglewood and Carson, backed by NFL team owners, have overshadowed the AEG plan.

“We would always prefer to have an excellent site in the mix, but we recognize that it is not in our control,” said NFL Executive Vice President Eric Grubman, the league’s point man on the L.A. market.

In January, St. Louis Rams owner Stan Kroenke and his partners revealed plans to build an 80,000-seat stadium at the former Hollywood Park site in Inglewood. The San Diego Chargers and Oakland Raiders said last month they have joined on a competing proposal in Carson. Those projects are moving forward, although no team has announced plans to relocate.

Billionaire Ed Roski has not spoken to the NFL in more than a year about his proposal in the City of Industry, effectively putting that option out of the running.

Farmers Field, proposed in April 2010, was to be built where the West Hall of the Convention Center now sits. Eight years earlier, AEG had dropped plans for a football stadium on the other side of Staples Center.

Although AEG says it no longer has designs on an NFL stadium, the company has been marshaling a case against the Inglewood site. It also pointed out to Carson’s mayor that a stadium could affect AEG’s assets in the city, including StubHub Center, a sports complex it owns.

The company hired former Secretary of Homeland Security Tom Ridge, who produced a report criticizing the Inglewood stadium as being a potential safety risk and terrorist target because of its location on the flight path of planes arriving at Los Angeles International Airport.

Mark Rosenker, a former head of the National Transportation Safety Board, also hired by AEG, cited in a separate report a potential for accidents on landings and debris falling from airplanes.

Those claims have been dismissed by aviation officials, including the former Federal Aviation Administration official in charge of the region.

In a visit to The Times on Monday, Ridge and Rosenker repeated their assertions. They said AEG founder Philip Anschutz commissioned the inquiries out of concern for the well-being of the region’s residents.

“We’ll never be able to rebut those who say, ‘Well, [Anschutz] got the report he wanted,’” Ridge said. “No, he got the high-level risk report that’s predicated on facts. And if you’d have commissioned me, I’d have given you the same report.”

Before Kroenke unveiled his $1.86-billion stadium, Farmers Field was the most expensive L.A. proposal at $1.5 billion, and was the only project with a sponsor attached. Farmers Insurance in 2011 signed a 30-year, $700-million deal with AEG to buy the naming rights for the stadium, with the understanding that no money would change hands until the venue was built.

A year later, the L.A. City Council unanimously approved a deal with AEG that included using stadium revenue and other funds to finance a new $350-million wing of the Convention Center.

L.A. Mayor Eric Garcetti said Monday that the city’s priorities are accelerating the revitalization of downtown and improving the Convention Center.

“In terms of football,” Garcetti said, “we continue to stand with the fans — we would welcome a team anywhere in our region that delivers the greatest benefit to our communities and economy.”

Representatives of the Carson and Inglewood proposals declined to comment on AEG’s decision.

Anschutz was never entirely sold on the idea of building a football stadium; Tim Leiweke, the company’s former president, was the driving force behind the concept. Farmers Field was a particularly expensive endeavor because it required AEG to tear down and rebuild the West Hall, fit a stadium into a confined space and add a parking structure.

AEG needed two teams to occupy the stadium, and Anschutz needed to buy a discounted stake in one of them, to make the project financially worthwhile. With the values of NFL franchises escalating, in part because of a new labor agreement and record-breaking television contracts, there is no desire in the league to sell a team at a bargain price.

Last week, the company announced plans to add a 755-room hotel development at L.A. Live.

AEG’s L.A. Live — which includes the Nokia Theatre, Staples Center, hotels and restaurants — would probably be vying with the proposed Inglewood sports complex for the same entertainment dollars.

Fikre said the company also is concerned about Inglewood and Carson using ballot initiatives to approve the stadiums, instead of those sites going through the lengthy process of environmental review. AEG spent $27 million on a 10,000-page environmental review of the Farmers Field site.

Fikre said AEG might eventually support a stadium in Carson, “but we’re certainly not going to be supportive of a major project like that being jammed through in a rushed process.”