State and city officials said Tuesday night that they  would try to save the three northernmost blocks of the High Line when they  choose private developers for the western rail yards, but they made no promises.   
  
The Metropolitan Transportation Authority, which owns  the six blocks worth of rail yards in the West 30s, will be asking bidders to  submit two plans: one in which the sections of elevated track along  30th Street and 12th Avenue would be preserved and the  other in which they would be removed, according to city officials. The M.T.A. would  determine whether the lost profit from maintaining the train track would be worth  it. 
 
“The M.T.A. and the city support retaining the High Line,”  William Wheeler, the M.T.A.’s director of special project development and planning,  told the more than 150 residents who packed an auditorium rented for the  unveiling of the West Side rail yard plans. “But what the M.T.A. has to do is understand the assessment of risk and  reward from the developers to understand how it impacts or doesn’t or benefits  or doesn’t the returns we are going to get from the  properties.”
   
Mr. Wheeler received a healthy applause, and speakers  from Friends of the High Line,  a nonprofit  organization that has successfully campaigned to turn the southernmost 19 blocks  of the unused track into a park, thanked the M.T.A. for its support. But  officials said that preserving the High Line would likely add to the developers’  cost because it would require them to have to work around it. If the track was torn down, however, it would be replaced by a narrow raised park just like  the High Line in order to open up 30th Street. 
 
Affordable housing was the other major issue that arose  during the meeting, which gave the public its first public glimpse of the city’s  plans for the former Jets football stadium site. Regina Myer, a senior vice  president at the Hudson Yards Development Corporation, the city agency  overseeing the project, said that developers would devote “up to 20 percent” of  the rental units they built for low-income families, and that two other publicly  owned sites on the West Side, which would accommodate hundreds of additional  affordable apartments, were “under very very serious consideration for  affordable housing.”
   
About half of the 21 community members who spoke  afterward complained that the affordable-housing commitment was not great  enough, because it would only come out to be one-fifth of rental housing while  condominiums would likely be entirely market-rate. 
 
“We just want to live in our city,” said Marisa Redanty,  the president of the Manhattan Plaza Tenants  Association.
   
But city officials said afterward that it would be  better to put affordable housing on other sites because it will cost so much for  developers to build a platform over the rail yards. They also did not want to  detract from the proceeds that the M.T.A. would earn from the sale of the  development rights. 
 
The two halves of the rail yards—the eastern half was  rezoned two years ago—will accommodate between 2,400 and 5,800 new apartments,  according to the proposed zoning, and between 6 million and 9.4 million square  feet of office space. Officials said they had not figured out the limit to the  height of the office towers, but they spoke freely about towers that are between  40 and 60 stories tall. 
  
The buildings would likely be placed on the northern and  southern edges of the rail yards because an Amtrak tunnel goes through the center.