In a damp subway tunnel in East Harlem, city and state officials early yesterday hacked into a stone wall with ceremonial hammers, marking what transit officials said was either the third or fourth groundbreaking for the Second Avenue subway.

“This time is different, because we have the money,” Governor Spitzer said, addressing the elephant in the unused tunnel: the challenge of financing construction of the T line, whose completion has derailed twice already after funds ran dry.

The MTA still needs to secure $875 million to pay for the first section of the line, to run between 96th and 63rd streets at an expected cost of $3.8 billion. Those missing dollars should be included in the MTA’s next capital plan, a spokesman for the agency, Jeremy Soffin, said.

The two-track line that, if completed, would stretch to Lower Manhattan from 125th Street along Second Avenue, is expected to reduce congestion by about 13% on the overcrowded 4, 5, and 6 lines.

“Maybe Wall Street can help us build it,” the federal transit administrator, James Simpson, said yesterday, pushing the MTA to lobby the private sector for the missing dollars. Public-private partnerships are one option the MTA would consider to secure the money, the agency’s CEO and executive director, Elliot Sander, said.

Mayor Bloomberg was noticeably absent from the makeshift underground stage shared by Governor Spitzer, the Democratic speaker of the Assembly, Sheldon Silver, the City Council speaker, Christine Quinn, Rep. Carolyn Maloney, and Deputy Mayor Daniel Doctoroff.

“If this were the groundbreaking for the no. 7 line, Mayor Bloomberg would likely not have missed it,” the chief attorney for the Straphangers Campaign, Gene Russianoff, said, referring to another subway expansion project that is favored by the city and is competing with the Second Avenue subway for scarce MTA funds.

The mayor was in Cincinnati promoting anti-gun legislation. Scheduling difficulties meant that neither the Manhattan nor the Cincinnati events could be moved, a spokesman for Mr. Bloomberg, Stu Loeser, said.

In the mayor’s absence, Mr. Doctoroff said the city would “not relent” in finding funds for the project, even if “we will be tempted to lose sight” of the importance of completing the project.

Mr. Doctoroff last month sounded warning bells on funding for the train line. “If we don’t know where the money’s going to come from, it’s a pretty good indication that we many not end up with what we want,” he said at the New York Metropolitan Transportation Council’s annual meeting.

Construction crews are expected to start work on the Second Avenue subway April 23.