Washington, D.C. ? Senior citizens are knocking on senators’ doors. Lobbyists for the homebuilding and energy industries are burning up their telephone lines.

Interest groups ranging from vulnerable people who tug at lawmakers’ heartstrings to powerful contributors to their political campaigns have joined the push for $40 billion in add-ons to a House-passed economic stimulus bill.

The groups are leaning on wavering Republicans to support a $200 billion-plus economic aid package in the Senate, setting the stage for a politically vexing vote Thursday on the Democratic-written plan.

The economic stimulus bill that shot through the House in a burst of bipartisan agreement last week remained stalled in the Senate on Tuesday. Behind the scenes, the diverse coalition of lobbyists and grass-roots organizers seemed in perpetual motion.

Senior citizens were asking senators to support extending $500-$1,000 rebates to 20 million elderly people and 250,000 disabled veterans left out of the House plan.

Lobbyists for the homebuilding and energy industries were calling and e-mailing, eager to take advantage of lucrative tax breaks the measure provides for their sectors.