Analysts urged the administration to make clear quickly the scale of revisions, or risk getting embroiled in an row which could delay the launch of long-awaited market reforms.
Yushchenko, elected last month on a wave of mass protests against electoral fraud, says he has no intention of revisiting all post-Soviet privatisations and has said only three dozen cases might be examined.
Speaking in the western city of Lviv on Wednesday, the president repeated assertions that the list to be examined would be one-off with no mass plan to overturn deals. Yushchenko again cited as an example last year's sale of the Kryvoryzhstal steel mill.
But Tymoshenko, speaking after a cabinet meeting, said: "I have here a list prepared by the prosecutor general. This is the result of checks conducted by prosecutors general into privatisations over five years.
"There are more than 3,000 enterprises. From 2000, the prosecutor general has brought to light 3,000 cases of illegal privatisations. We will return to the state that which was illegally put into private hands."
The cases, she said, had been shelved owing to intervention from officials. Ukraine's previous leaders had "overseen these criminal dealings. In some cases there was no real competition, in others a low price was established."
Yushchenko, in comments reported by Interfax Ukraine news agency, meanwhile said the government's list could in no way be reopened at a later date or extended to other sites.
Oleksander Ryabchenko, head of the International Privatisation Institute, said Yushchenko's team should establish a clear framework to reassure international investors.
"It is so far unclear who they will go after: new owners who failed to fulfil investment obligations or institutions that broke laws in conducting the selloffs. It would be dangerous to cast doubt on the entire legal framework of selloffs," he said.
"It is vital to steer clear of talk of nationalisation. If deals are questioned, there must be clear criteria. A list of sites must be short and dates must establish when the process is to be completed."
Gleb Vishlinsky of the German-Ukrainian consulting company GfK-USM said Yushchenko and Tymoshenko owed it to investors to present their views publicly and together.
"If they do not present a list, a final list, it will limit investment," he said. "Current and potential investors cannot live with the notion that any factory could come under the threat of legal action."
Tymoshenko's cabinet has already annulled all decisions allowing a deal privatising the Kryvoryzhstal steel mill, sold in dubious circumstances last year, to proceed. But no details of the government decisions have been made public.
Kryvoryzhstal was sold for $800 million - a sum experts say was below its market value - to a consortium with close ties to Ukraine's former leadership.
Tymoshenko said only that sites to be subjected to a review would "not be as large as Kryvoryzhstal".
Yushchenko said he believed Kryvoryzhstal could fetch more than $3 billion in any new selloff.