New York City put out a call Wednesday for builders interested in its long-delayed Seward Park project, which would transform the largest parcel of underdeveloped publicly owned land in Manhattan below 96th Street. The project could bring up to 1.65 million square feet of housing, retail and office space to the Lower East Side. The site near Delancey and Essex streets has been at the center of more than four decades of bitter disputes since the city demolished tenement buildings as part of an urban-renewal effort. Community groups and the city struck a deal last year to include 900 units of new housing, only about half of which are market rate — a virtually unprecedented proportion of affordable housing. The plan received City Council approval in October, which increased the number of units to 1,000. It remains to be seen how developers will view the daunting task of creating a huge residential and commercial complex with such a large affordable-housing requirement.