Senate Democrats plan to hold a special caucus on health care reform at 5 p.m. Wednesday to discuss a tentative deal on how to change the bill’s public insurance option.

A group of 10 Democrats — five centrists and five liberals — agreed Tuesday night to send a set of proposals to the Congressional Budget Office for an official score, but the details have yet to be presented to all 60 Members of the Democratic Conference.

However, it’s unclear how much information Senate Majority Leader Harry Reid (D-Nev.) and the 10 members of the group can share with their colleagues because the CBO has asked Reid to keep mum on the details if he wants them to provide him with a confidential score.

However, sources said the thrust of the deal tracks closely to news reports on the six days of the group’s negotiations.

It appears that the provisional agreement would jettison current provisions creating a public insurance option that permits states to opt out. Instead, the Office of Personnel Management would essentially run government-sponsored insurance exchanges in which private companies would be allowed to compete for uninsured and small-business customers. The OPM would be tasked with making sure the companies that participate follow strict rules, such as restrictions on the profits that they could earn.

Democratic sources said there is still some confusion — even among participating Senators — over whether the proposal that moderates and liberals agreed to send to the CBO would include a “triggered— public option.

One source said it appears the last sticking point in the group was whether to include a provision that would allow the government to create a public plan if private insurers decline to participate in a government-sponsored exchange. The compromise proposal includes an exchange that would allow insurers to compete for uninsured and small-business customers, but it would prohibit private companies from making more than a minimal profit.

The source said it’s likely the group will send two trigger proposals to the CBO — one that would be a public option and one that would be state-based. In a statement Tuesday night, one liberal member of the group, Sen. Russ Feingold (D-Wis.), said he would have trouble supporting the proposal if it does not include some form of a public option.

“While I appreciate the willingness of all parties to engage in good-faith discussions, I do not support proposals that would replace the public option in the bill with a purely private approach,— Feingold said. “We need to have some competition for the insurance industry to keep rates down and save taxpayer dollars. I will base my vote on the bill on the entirety of what is in the bill, and whether I think the bill is good for Wisconsin.—

However, including a trigger or any other version of a public option could prevent Sen. Joe Lieberman (ID-Conn.) from voting for the bill. He has threatened to filibuster a bill that includes any form of the public option.

Reid needs 60 votes to overcome a GOP-led filibuster, meaning he will have to persuade all Democrats to support it or find a handful of Republican defectors. He is courting the two centrist Maine Republicans, Sens. Olympia Snowe and Susan Collins.