Jim Messina, the Obama campaign manager, can be foul-mouthed. But readers would not know it because he deletes the curse words before approving his quotes. Brevity is not a strong suit of David Plouffe, a senior White House adviser. So he tightens up his sentences before giving them the O.K.

Stuart Stevens, the senior Romney strategist, is fond of disparaging political opponents by quoting authors like Walt Whitman and referring to historical figures like H. R. Haldeman, Richard Nixon’s chief of staff. But such clever lines later rarely make it past Mr. Stevens.

Many journalists spoke about the editing only if granted anonymity, an irony that did not escape them. No one said the editing altered the meaning of a quote. The changes were almost always small and seemingly unnecessary, they said.

Those who did speak on the record said the restrictions seem only to be growing. “It’s not something I’m particularly proud of because there’s a part of me that says, ‘Don’t do it, don’t agree to their terms,’ ” said Major Garrett, a correspondent for The National Journal. “There are times when this feels like I’m dealing with some of my editors. It’s like, ‘You just changed this because you could!’ ”

It was difficult to find a news outlet that had not agreed to quote approval, albeit reluctantly. Organizations like Bloomberg, The Washington Post, Vanity Fair, Reuters and The New York Times have all consented to interviews under such terms.

“We don’t like the practice,” said Dean Baquet, managing editor for news at The New York Times. “We encourage our reporters to push back. Unfortunately this practice is becoming increasingly common, and maybe we have to push back harder.”

The Obama campaign declined to make Mr. Plouffe or Mr. Messina available to explain their media practices. “We are not putting anyone on the record for this story,” said Katie Hogan, an Obama spokeswoman, without a hint of irony. She pointed to the many unrestricted interviews with campaign officials every day on television and when the press corps travels with the president.