WASHINGTON — Top congressional leaders said Tuesday that negotiators are making slow but steady progress on a must-do spending bill to prevent a government shutdown next week and fund the battle against the Zika virus. Some tricky issues remain, but optimism was building that an agreement might be unveiled in the next day or two.

Congressional aides said that progress included an offer from Republicans to drop especially controversial provisions that would have eased pesticide regulations under the Clean Water Act and blocked tighter regulations on the length of workweeks for truckers.

But the Senate’s top Democrat says a battle continues to rage over a demand by Senate Majority Leader Mitch McConnell of Kentucky to make sure corporations do not have to disclose their spending on political activities to investors. Minority Leader Harry Reid, also said his party is fighting a move by Senator Ted Cruz to block the government from ceding control over some of the internet’s key systems — namely, the directories that help web browsers and apps locate information on the web.

Negotiators are also continuing to grapple over which spending cuts would accompany the $1 billion-plus in Zika funding — and how big they should be.

Reid complained that GOP negotiators were blocking a Democratic request for money to help Flint, Michigan, repair its lead-tainted water system. The fate of Louisiana flood aid seemed iffy as well, aides said.

The roster of often arcane issues are coming into play because the stopgap spending measure — it would keep the government running into December — is the last piece of must-do business facing Congress before it recesses for the fall campaign.

Associated Press