New York is a tough town -- and getting tougher.

The average monthly rent in the four boroughs minus Staten Island crept above $3,000 last year -- compared with about $1,000 nationally. The spread runs from $1,150 in the Bronx to $3,860 in Manhattan.

And here's the worst part. Rent is chewing through monthly incomes in the city at an ever more ravenous rate. New Yorkers in 2000 spent about 24 percent of their income on rent. Today they're spending 40 percent.

In a city with a poverty rate of 21 percent and a median household income of $51,000, we have some work to do.

The challenge is this: We must remain a place where newcomers -- with a reasonable amount of ingenuity and effort -- can steadily climb into the middle class.

That has been New York's role for four centuries, but now it appears endangered. That's not good for any of us.

What to do?

Build more affordable housing. Mayor Bill de Blasio has wisely made this a signature goal, promising to build or preserve 200,000 affordable units in the five boroughs over the next 10 years.

Build a reliable health-care system -- attuned to modern medical economics. That means fewer outdated hospitals with hundreds of empty beds and far more neighborhood clinics dedicated to primary care and other specialties. The mayor has been on the wrong side of this one.

Build more good jobs with decent pay -- from new tech startups to modern manufacturing enterprises.

Build a public education system that works for all of us. That means a globally competitive public school system and a first-rate city university system that is able to keep tuitions affordable.

This we don't need: a town where resentments between rich and poor are intentionally heightened.

With his "tale of two cities" scenario, the mayor has come foolishly close to doing that. But consider this: The city's Independent Budget Office said this week that in 2011 the top 1 percent paid 46 percent of city income taxes.

Without them? It's harder for the rest of us to move up.