WASHINGTON — A top adviser to Senator Obama is describing Senator Clinton as a “veteran of nondisclosure” as the Illinois senator’s campaign steps up its attacks on the former first lady over the issue of transparency.

In a conference call yesterday, the Obama campaign called on Mrs. Clinton to release a trove of documents that she has failed thus far to make public, including her most recent tax returns, the funding projects she has requested as a senator, a list of all donors to President Clinton’s library and foundation, and White House records from her time as first lady.

“The truth is she is a veteran of nondisclosure,” Mr. Obama’s chief strategist, David Axelrod, told reporters.

An Obama campaign spokesman, Robert Gibbs, added that Mrs. Clinton’s delay in releasing the documents raised even more suspicions.

“What is Senator Clinton hiding and what is lurking in those documents that she does not believe voters have a right to know?” he said.

The Clinton campaign held its own conference call less than an hour later, and advisers accused Mr. Obama of negative campaigning and attacking Mrs. Clinton’s character.

“Rather than build Senator Obama up, they have chosen to tear Senator Clinton down,” a spokesman for Mrs. Clinton, Howard Wolfson, said.

While largely deflecting questions about the documents the Obama campaign is demanding, he in turn suggested that Mr. Obama had been less than forthcoming about several issues and called on him to release tax returns and funding requests from earlier in his career.

“This works both ways,” Mr. Wolfson said. “If we’re going to talk about disclosure, let’s talk about it.”

The Clinton advisers had seized on a report in the Chicago Tribune that Mr. Obama is preparing a “full assault” on Mrs. Clinton that calls into question her ethics and transparency.

Yesterday’s bickering underscored strategic choices by each campaign. Mr. Obama’s camp appears to be banking on the notion that characterizing Mrs. Clinton as secretive will resonate with voters wary of returning to the battles of the 1990s.

And the Clinton campaign has been quick to point out any hint of negativity from the Obama campaign as a way of undermining the contention that he represents “a new kind of politics.”