AUGUSTA — Maine lawmakers opened their 2012 session today, welcomed by a State House full of citizen lobbyists facing a full agenda for the next 3½ months.

The House and Senate will conclude business left unfinished during the opening round of the 125th Legislature last year. Energy, education and voting rights are among the issues on the table, but the budget will be center stage in the opening weeks of the session.

Amid the formalities of resuming business, the State House hallways were crowded with groups out to make their presence known. Unions affiliated with the AFL-CIO sent members to show their concern over bills dealing with workers’ compensation, a right-to-work measure affecting public sector workers and unemployment insurance.

Also, roughly a dozen members of the Occupy movement, many of whom were involved in the encampment at Capitol Park during the fall, said they intend to have a presence in the State House this year to express their views on energy and importation of solid waste.

In addition, lawmakers planned to seat for the first time a member of the Maliseet Indian tribe, David Slagger. Members of three other tribes are already represented in the Legislature.

In major business to be taken up early in the session, Gov. Paul LePage wants to balance the state budget by making up for a gaping $200 million-plus shortfall in the Medicaid program that’s expected to develop in the next year and a half.

Lawmakers will also meet Thursday and Tuesday before they depart for their three-day Maine Development Foundation bus tour to southern and western Maine businesses and educational institutions.