BOSTON -- As Gov. Deval Patrick on Thursday threatened to veto a $500 million tax proposal to fund transportation, Senate Democrats were locked in a nearly four-hour private caucus where it appears a range of opinions were expressed.

The plan top House and Senate Democrats proposed on Tuesday received a dressing down Thursday by Patrick, who called it a "fiscal shell game" and said he would veto the legislation if it reached his desk. Patrick has called for a $1.9 billion tax proposal to fund transportation and education.

"There's a chance that you get nothing if that happens," Senate Ways and Means Chairman Stephen Brewer said, referring to Patrick's veto threat. Brewer said he was sticking by the $500 million plan, and was mum on how discussions progressed in Senate President Therese Murray's office.

While other Democratic senators involved in the marathon discussion also declined to speculate on parameters of potential Senate changes to the bill, lawmakers expressed a range of opinions on the legislation after emerging from Murray's ornate office.

"South Coast Rail is not funded in the package, so there is no way that you can look at any of this from a southeastern Massachusetts perspective and think that a bond bill down the road or anything like that could take care of the issue," Sen. Marc Pacheco, D-Taunton, said of the legislative leaders' proposal. "I'm not really interested in it at all. I mean, it just really doesn't get us where we really need to be."

Sen. Jennifer Flanagan, D-Leominster, had concerns about taxpayers who would fund the spending.

"People are concerned. There's a genuine concern about how much taxpayers can afford, versus what the needs are of the commonwealth," Flanagan said. "There are clearly some transportation needs that need to be addressed throughout the commonwealth, not only with the T but roads and bridges."

Sen. Jamie Eldridge, D-Acton, who supports the governor's plan, was among a few senators who said the amount of new revenue should be increased.

"I just think this is a really unique moment in time when we can really invest," said Eldridge. "Clearly there's a diversity of opinion."

"There are some things in the plan that I like, but overall I think it is not adequate to the need, either in transportation just as its own bucket, and certainly not for the other areas of human infrastructure," said Sen. Sonia Chang-Diaz, D-Jamaica Plain.

"Maybe we need a little more," said Sen. Will Brownsberger, D-Belmont.

Other senators said they were still formulating opinions.

"I'm still looking at that. I don't know," Sen. Ken Donnelly, D-Arlington, said. "I want to see what comes out of the House."

"It's a very significant tax increase," said Sen. Brian Joyce, D-Milton. "There is no question but that we need to make investments in our infrastructure. It's a problem that took a long number of years to develop, and we can't address it overnight."