NEWARK, N.J. — The public was to get its first detailed look at the Port Authority of New York and New Jersey’s $1.7 billion plan to extend PATH train service to Newark Liberty International Airport, a project that has engendered debate inside the agency over whether it should be shelved in favor of other initiatives.

The public comment session scheduled Tuesday night was to be the first of two in New Jersey’s largest city, signaling the beginning of a mandatory environmental permitting process expected to take about 18 months. After that, construction is expected to take several more years.

Currently, PATH trains from lower Manhattan, where the World Trade Center is located, terminate at Newark’s Penn Station and airport travelers switch to New Jersey Transit trains. That has prompted some officials at the Port Authority to criticize the project as redundant and unnecessary.

A year ago, then-Port Authority board member Kenneth Lipper called the PATH extension and a proposed rail system feeding LaGuardia Airport in Queens “the rails that will serve no one,” a play on Alaska’s infamous “bridge to nowhere.” Lipper claimed the train to Newark would carry only between 1,000 and 3,000 passengers daily.

A Port Authority spokesman said Tuesday the agency, which runs the region’s transit hubs and owns the World Trade Center site, doesn’t have an accurate ridership estimate for the Newark route but expects to have one by early next year.

The rail project is competing for dollars along with a smorgasbord of large-scale Port Authority projects, including a proposed new bus terminal in midtown Manhattan and new rail tunnels under the Hudson River. The bus terminal project, estimated to cost between $7 billion and $10 billion, has been mired in political squabbling between New York and New Jersey officials.

Supporters of the PATH-to-Newark project include Newark Mayor Ras Baraka, who has touted the proposed new station, which would sit west of the airport in Newark’s South Ward, as a potential engine for revitalizing the neighborhood. He said it would have “an enormous impact on Newark’s economy and that of the region” by spurring housing and economic development.

The new station also could be used by commuters to travel directly into Jersey City or lower Manhattan, potentially easing crowding at Newark’s Penn Station and in downtown Newark. That would necessitate acquiring land around the proposed station, currently inhabited by warehouses and other light industry, for parking.

Tom Wright, the president of the Regional Plan Association, an urban planning think tank, said extending the PATH to Newark would provide “an opportunity for redevelopment and for taking cars off downtown streets in Newark.”

“We would like to see it combined with local planning so it benefits the South Ward and local residents,” Wright said. “It doesn’t work just as a benefit for investment bankers from lower Manhattan going out to Newark Airport.”