Despite Wall Street warnings, Gov. William Weld said Wednesday that he is determined to consider a plan to merge the state's independent transportation authorities and state agencies into a single "super-authority" to subsidize mass transit.

The idea of combining the autonomous port and turnpike authorities with the deficit-ridden Massachusetts Bay Transportation Authority and state highway and transportation agencies prompted a negative response from New York bond rating agencies when it surfaced two weeks ago.But shortly after unveiling his 1993 budget, Mr. Weld indicated in an interview that he has not given up on the plan.

"We want to go ahead with considering it. Nobody expected it to be the first choice of the rating agencies, but we're not going to do it in a way that's going to impair the obligation to bondholders of any existing authorities," Mr. Weld said.

Aides to Mr. Weld say the major benefit of the idea is that it would get the annual liability of the MBTA, variously pegged at $200 million to $400 million, off the state's budget. A second advantage, they say, is that it would allow policy-makers to consider all transportation alternatives under one roof.

"We're not going to act hastily. We're not going to act irresponsibly. But I do want to consider whether a consolidation of those agencies would promote greater efficiencies," said Mr. Weld.

The move may have already gone beyond consideration, however. The governor's budget for the coming year reportedly assumes a $42-million boost

from implementation of the plan. Administration officials could not be reached for comment Thursday.

Officials at the Massachusetts Port Authority and the state's turnpike authority have been highly critical of the scheme, arguing that it would drag down their bond ratings. When asked if it would raise Massport's cost of borrowing for a $1.5-billion expansion of Logan International Airport, Mr. Weld replied abruptly.

"What can I tell you? If it turns out not to be a good idea, we won't do it," the governor snapped.

The authority plan comes at a time of increasing attention to Mr. Weld's style of shooting from the hip and airing public policy options in public. Reporters and legislators are also puzzled by Mr. Weld's new $14-billion budget that promises both spending increases and tax cuts.

One legislative leader expressed serious doubts that the plan would ever fly.

"I don't see that it makes sense policy-wise," said House Speaker Charles F. Flaherty Jr., who was also interviewed at Harvard University's John F. Kennedy School of Government. Both Massport and the Massachusetts Turnpike Authority "have a mission and they're fulfilling that mission," the Cambridge Democrat said.

When asked whether the plan could ever win support in the House, Mr. Flaherty replied, "Maybe it could if you made a case for it but I don't know how you would make a case for it."