WASHINGTON — Facing a weekend deadline to avoid a government shutdown, a combative Congress appears on track to advance a massive $1 trillion-plus yearend spending package that curbs agency budgets but drops many policy provisions sought by GOP conservatives.

Lawmakers reached a tentative agreement on the measure. It chips away at the Pentagon budget, foreign aid and environmental spending but boosts funding for veterans programs and modernizing the nuclear arsenal.

The measure implements this summer’s hard-fought budget pact between President Obama and Republican leaders. That deal essentially freezes agency budgets, on average, at levels for the recently completed budget year.