It took months of negotiations, countless meetings and days of private sessions, but the Bellevue City Council on Monday gave unanimous support to a light-rail agreement to fund a tunnel through downtown.

The 7-0 vote was a proud moment for the council, which has been marred with struggle over placement and cost of East Link light-rail for the last few years.

“We’ve had a few frayed nerves and a few loud voices but we’ve kept our eyes on the prize,” said Bellevue Council Member Grant Degginger.

The prize is a tunnel that could cost in excess of $300 million and keep the train from disrupting downtown activity. Bellevue is on the hook for as much as $160 million, but the city plans to work with Sound Transit to cut costs, and its contribution as well.

Bellevue will contribute $100 million to the tunnel in 2014, primarily in donation of land and projects that will help Sound Transit. The city will likely have to shave funds off other projects, or take a look at property tax increases to pay the full $100 million.

The rest of the money is a contingency cost that will only be spent at the end of the project, and could be eliminated if it comes in under budget.

Council Members Degginger, Kevin Wallace and Jennifer Robertson and Bellevue staff have negotiated extensively with Sound Transit over the past few months to get a more favorable deal, after Sound Transit chose a route the majority of the Bellevue council did not favor. Through this negotiating period, which has lasted since July when Sound Transit chose to run the rail on Bellevue Way and 112th Avenue, the two sides agreed on a raised flyover that eliminates all street-level crossings from Seattle to the Bel-Red corridor. Bellevue also pledged that nearby residents won’t see a train land feet from their doorsteps.

“The people who own homes on Southeast Eighth and 112th are going to end up with a full take, there’s not going to be a sliver take, end of story,” Wallace said.

While the agreement constitutes an important step forward, there are still numerous unanswered questions, surrounding Bellevue’s method of payment and the final cost that left some council members skeptical.

The agreement features several “off ramps” wherein both parties can back out. The city has an out if Sound Transit refuses to adopt the city’s requested design changes. Sound Transit can drop the agreement if Bellevue does not grant a number of permitting changes by the end of 2012, according to the agreement.

But that would likely mean an outcome no one wants, trains running through downtown streets, Deputy City Attorney Kate Berens said.

Sound Transit and Bellevue will now work closely to make sure this scenario never becomes a threat. After contentious discussions in the council, and between Bellevue and Sound Transit, representatives were very complimentary of fellow council members, as well as Sound Transit staff. Council members hoped this would mean the beginning of a strong relationship between the two sides to create an alignment that will make everyone happy.

“We are essentially engaged and married to Sound Transit on this, and no marriage succeeds without hard work,” Council Member Claudia Balducci said.