A hotel-tax hike the Chargers want to pitch to voters in November would finance a $1.8 billion stadium and convention center downtown, with money left over for operations, tourism marketing and San Diego’s general fund, said advisers to the team in a briefing for reporters late Tuesday.

As reported last week, the team’s plan would raise the city’s tax on hotel stays to 16.5 percent from 12.5 percent. Some hotel owners worry that the higher rate could deter visitors, while others note comparable taxes in competing cities such as Anaheim and San Francisco.

In San Diego, the proposed tax hike would support $1.15 billion in publicly issued bonds, with $350 million for the city’s contribution to building a football stadium near Petco Park, $600 million for an adjoining convention center, and $200 million to buy land. No money is planned to upgrade nearby roads.

The remaining funding — $650 million — would come from the Chargers and National Football League . The team would contribute $350 million, presumably raising some of that money by selling “seat licenses” to fans and stadium naming rights. The NFL would kick in $300 million, made up of a $200 million loan and $100 million grant.

The Chargers released the full text of their proposed ballot initiative Wednesday morning, which will be followed by publication in Thursday’s print editions of The San Diego Union-Tribune as a legal notice. The publication triggers a 21-day waiting period, after which the team can begin gathering signatures to qualify the initiative for the November ballot.

Less clear is what percentage of the electorate would be required for passage.

On March 18, a state appellate court ruled that a citizens initiative to tax marijuana dispensaries in Upland needed approval by a simple majority (50 percent plus one vote), potentially lowering the two-thirds requirement that has doomed many similar initiatives over the years in California.

However, the team is proceeding on the assumption that the old rules will apply. “We’re operating as if it’s two-thirds,” Fred Maas, a development consultant to the Chargers, said Tuesday.

Winning approval at either threshold will be difficult without political support from a variety of San Diego’s key opinion makers, Chargers advisers have freely acknowledged. Major potential opponents and supporters, including Mayor Kevin Faulconer , have declined to comment until the team released the final initiative.

After a vote last week, the San Diego Regional Chamber of Commerce Board said it was open to the Chargers’ concept of a combined downtown stadium and convention center, but it wanted a closer look at the details. City Councilman David Alvarez expressed skepticism, saying the plan as outlined “will not put the public first.”

Chargers advisers described the financing plan as conservative, with “shock absorbers” designed to assure bond investors of repayment during economic downturns, as well as provide $25 million a year (in 2017 dollars) to operate and maintain the complex, plus $4 million for a capital fund for future upgrades or major repairs. The team would contribute $15 million for stadium operations and maintenance.

The initiative also proposes to generate revenue for tourism marketing, replacing a 2 percent surcharge on room rates that is being challenged in court as an illegal tax hike because it was approved by hoteliers and not the general public.

A city-controlled tourism marketing fund would get the first 1 percent of the tax on room rates. The second 1 percent would be available only after a reserve for “debt coverage” was established.

Team advisers said the risk of shortfall is low for the hotel industry’s tourism fund, because the tax money would start to flow on Jan. 1, 2017, and build up quickly in the years before construction started.

Indeed, the Chargers forecast calls for the city’s general fund to receive $5.3 million in 2017, rising to $8.9 million by 2019, before falling to zero in the first year of construction as operating and maintenance reserves are funded. Then it would rise again until the bonds were repaid, a period estimated at 33 years or more from 2017, at which point the tax would fall from 16.5 percent to 13.5 percent.

The Chargers would agree to lease the stadium for 30 years, starting when construction was finished, in addition to not relocating for 30 years. The complex would be owned and operated by the city, probably through a joint-powers authority, with the team keeping only game-day and NFL-associated revenue.

The project would be situated on a 15-acre site that encompasses the city-owned Tailgate Park, as well as three private parcels, and a block used as a bus yard by the Metropolitan Transit System. The transit agency already has reached out to the Chargers about initiating negotiations to sell the property and find a replacement site for the maintenance yard.

As for the design of the project, the stadium portion would include about 65,000 seats — expandable to 75,000 during Super Bowls — as well as luxury suites and other amenities.

The new convention center would total about 385,000 square feet, including the 225,000 square feet of exhibit space envisioned in the city’s plan to expand its convention center toward San Diego Bay, a project that’s been stalled because the plan to finance it with a hotelier-approved room tax increase was ruled unconstitutional.

Still undecided, though, is whether the convention center would sit below the playing field or alongside the stadium.

Maas, the Chargers development adviser, said preliminary studies showed that stacking the stadium above the convention floor would be “very expensive.” He said the team hopes to reach key architectural and engineering decisions in about a month.

In January, the NFL’s owners voted to allow the Chargers to share a $2.6 billion stadium in Inglewood being built by the St. Louis Rams. That same decision gave the Chargers until January 2017 time to instead pursue a stadium deal in San Diego, with a one-year extension if a November ballot initiative was approved by voters.

dan.mcswain@sduniontribune.com (619) 293-1280 Twitter: @McSwainUT