Republicans are advancing a plan to add up to $150 billion for the Pentagon as part of the party’s megabill on spending and tax cuts. But that increase is spread over a decade — not enough, defense-oriented Republicans argue, to substitute for large, sustained annual budget hikes.

In his first full budget proposal since returning to the White House, President Donald J. Trump has laid out a sweeping $1.7 trillion spending blueprint that slashes domestic programs to levels not seen since the 1960s,