Schumer has endorsed Gillibrand and said he wholeheartedly supports her 2010 Senate bid.
An adviser to Rep. Carolyn Maloney, D-N.Y., said last week she plans to challenge Gillibrand and would be announcing her candidacy in upcoming weeks. Her entrance would create a potentially contentious and expensive primary battle.
Schumer said he's spoken with Maloney in recent days, but not about whether she would run. He said he doesn't anticipate asking Maloney not to.
"I think she's going to have to make that decision for herself," Schumer, a Democrat who is New York's senior senator, told reporters and editors from The Associated Press.
Paul Blank, an adviser to Maloney, said he respects Schumer, and that Maloney made her decision to run because she feels voters need a choice.
Gillibrand was appointed earlier this year to fill the seat left empty by Sen. Hillary Rodham Clinton's appointment as secretary of state. The White House supports Gillibrand's candidacy.
Schumer said Gillibrand is popular and effective in the Senate. He said he plans to help her in any way he can.
"I'm not trying to be heavy-handed in any way. I'm not ... calling people up and saying don't support somebody else. I'm just doing it in a positive way," Schumer said.
Also, Schumer said he doesn't intend to intervene to help end the monthlong standoff in the New York Legislature. He said he's urged both sides to get together to pass top-priority legislation, but he thinks it needs to be resolved among state lawmakers.
"I don't think anyone can force it," Schumer said.
The standoff is between a Republican-dominated coalition that voted June 8 to overthrow the Democratic conference. But a day later, the coalition lost one of its two dissident Democrats who returned to the Democratic conference, leaving the Senate knotted 31-31. The Democratic conference won the Senate majority in the November elections.