The three citizens' groups that have threatened to sue the state over various aspects of its Central Artery Project will all carry through with their promised litigation in time to meet today's filing deadline, representatives of the organizations said yesterday.

The Charles River Watershed Association, Boston's Committee on Regional Transportation (CRT) and the Sierra Club have all decided to bring suit against various state agencies to ensure that the plans for the $5 billion Central Artery Project are enviornmentally sound and that the state's approval process is monitored properly.

Two of the groups--the CRT and the Watershed Association--are taking legal action principally to block Scheme Z, the highly controversial design for a mammoth 11-story, 16-lane highway interchange over the Charles River in East Cambridge.

The CRT is charging the Commonwealth with violating Massachusetts environmental policy standards with its designs for Scheme Z and other sections of the state's portion of the interstate highway system, said Rob J. Garrity, a CRT director. The group filed suit against the state Department of Public Works (DPW) yesterday.

The Charles River Watershed is suing the DPW on the grounds that the department did not thoroughly examine alternatives to Scheme Z prior to drafting its final report on the Central Artery Project, said Karen Pelto, the group's environmental affairs coordinator.

"A suit is really the only option left to us to preserve our rights to seek further change in the process," Pelto said.

She added that the litigation is in part a bargaining tactic to force the state to consider objections and examine alternatives to Scheme Z. "We don't think it needs to be a legal solution," Pelto said.

The Sierra Club is filing suits against three other state agencies besides the DPW. According to Priscilla A. Chapman, director of the New England chapter of the Sierra Club, the state did not comply with Massachusetts environmental policy regulations in its review of some potential hazards related to the proposed Central Artery.

Specifically, Chapman said the state did not perform thorough enough tests on ventilation stacks which would remove emissions from the underground tunnels and disseminate them through the air above ground.

Chapman said she was disappointed that the state had not responded to the intention to sue notice that the Sierra Club filed two months ago. "I'm not aware of anything that has changed since the day we filed the notice and now," she said.

Garrity said his group is also suing the state to penalize the state for its "gross negligence" throughout the process.

He said the fact that the state-run process has only been monitored by state agencies is tantamount to "letting the fox guard the hen house." "We have to be in essence the watch-dog here," he said.

At a meeting Monday night, the Cambridge City Council decided to carry through with its promise to sue the state to keep Scheme Z away from Cambridge.

"There's a whole group of people in East Cambridge whose lives are being threatened" by the project's potential enviornmental impact, Councillor Timothy J. Toomey Jr. said at the meeting.

The groups now have 90 days to decide whether to carry the suits to the federal level.