PRINCETON, Oregon — Tensions have run high in eastern Oregon since an armed group seized the headquarters of a national wildlife refuge early this month, but the primary opponents in the standoff have been pretty clear cut: The antigovernment protesters are facing off against law enforcement agents, who are trying to figure out a peaceful end to the illegal occupation.

But in recent days, as the standoff has dragged toward its third week, a new element has been added to the chemistry: counterprotesters who are converging here to denounce the occupying faction — in person at the refuge headquarters — and demand that federal public lands remain open for all. The newcomers include environmental activists, retired federal workers and a couple of long-distance hikers.

“We’re here to say the Malheur is not occupied by the militia — we’re here, we’re on the land,” Kierán Suckling, the executive director of the Center for Biological Diversity, an environmental advocacy group in Tucson, Ariz., said Tuesday during a rally at the refuge. About a dozen people joined him, from places like Eugene, Oregon and Spokane, Wash., and waved signs at passing vehicles.

The advent of a new assortment of outside protesters has again shifted the dynamics of the situation at the Malheur National Wildlife Refuge. At first, when a band of armed men and women led by Ammon and Ryan Bundy seized the refuge’s headquarters, they sought support from the local community for their demand that millions of acres of federal land be placed in local, state or private hands. Instead, community leaders asked the Bundy group to leave. F.B.I. agents and sheriff’s deputies from around Oregon then converged in the nearby town of Burns.