The Regional Plan Association formally opposed construction of the proposed New York Jets football stadium on the West Side yesterday, resisting pressure from City Hall and becoming the first major civic group to openly criticize the city- and state-backed plan.

The proposed stadium, known as the New York Sports and Convention Center, “represents a suboptimum use of a site that is key to the long-term development of the district,” the association’s report said. “There is no compelling need to place this in a part of the city that should be devoted to high value, high-density office and residential development.”

After news leaked last month of the powerful private planning group’s opposition to the stadium, board members began fielding calls from stadium supporters in a bid to reverse the group’s position. The 56-member board has an advisory role, with the staff members formulating the group’s policy positions.

“People who were strong advocates of the stadium called us expressing their points of view, which mainly rested on the fact that the Hudson Yards plan was a package, and you couldn’t take one piece out with having the whole thing crumble,” said Barbara Fife, a deputy mayor in the Dinkins administration and a member of the association’s board.

“When I was chairman of the [Metropolitan Transportation Authority], the RPA published a number of reports which I intensely disliked, and it never occurred to me to call any members of the board about it,” said board member Richard Ravitch.

Other prominent civic groups have not touched this hot political potato, including the Citizens Budget Commission and the Municipal Art Society, which sidestepped the stadium issue to confront the less controversial expansion of the Jacob K. Javits Convention Center.

“The RPA staff, failing to reflect the diversity of opinions of their board, has taken a lead role in attacking the first economically viable plan for the Hudson Yards which will lead to both short term and long term job creation; the revitalization of an underdeveloped neighborhood; unparalleled waterfront access, and 15 acres of new public space,” said a Jets spokeswoman, Marissa Shorenstein.

“The city’s plans for the Far West Side are emblematic of the type of vision and planning that the RPA should be supporting, but instead the RPA staff has put forward assertions in its report that are simply not supported by analysis or fact,” a spokeswoman for Mayor Bloomberg, Jennifer Falk, said in a statement.

Other than its opposition to the stadium, and a three- to five-year lag in some key developments, the report backs much of the Hudson Yards plan set out by Mayor Bloomberg and supported by Governor Pataki, including the rezoning of the area, extending the no. 7 subway, and building platforms over the area’s rail yards.

Under the association’s timeline, the city would proceed with low-cost changes, deferring the big-ticket items until 2010 when some private development has taken hold.

“This will offset some of the city’s financial risk,” said the association’s president, Robert Yaro.

It will also give Lower Manhattan more time to recover before having to compete against new office developments on the West Side and give the Second Avenue subway a head start before the no. 7 line. The association thinks the Second Avenue line is more critical for easing commuter congestion.

“The Jets suggest the choice is a stadium or a hole in the ground,” Mr. Yaro said. “I disagree. If you get the zoning right, you will see development almost immediately on the eastern half of the area and a number of alternatives” will begin to develop for the rail yards.

During the first phase, the area would be rezoned for residential development by early next year, and by 2009 the northward expansion of the Javits Center and the creation of public parks would be complete.

A mixed-use alternative for the Western Rail Yards should be developed during this time, to be completed during the second phase of the development. Stressing the need for residential housing, the report said the rail yards “is ideally suited for high-density residential development that would take advantage of its waterfront location and Manhattan’s persistent demand for new housing locations.”

The $600 million investment by the city and state proposed under the Hudson Yards plan to build a platform over the yards should be sufficient to spur this private development.

The second phase would run from 2010 to 2015 and include the development of the Eastern and Western Rail Yards and the extension of the no. 7 subway to a new station at 34th Street and 11th Avenue. The third and final stage would take place from 2016 to 2020 and include building over the Lincoln Tunnel infrastructure in the area and a second no. 7 station at 41st Street.