JAKARTA, Indonesia — Last September, ultraconservative Islamic groups telegraphed their power, railing against an international beauty contest until the government ordered it to be staged entirely on the Hindu resort island of Bali. In 2012, radical Islamic groups known for their violent tactics and religious conservatives raised enough of a fuss that Lady Gaga canceled a concert here in the Indonesian capital. And hundreds of local governments in recent years have passed rules on morality and dress inspired by Shariah, or Islamic law, and instituted bans on alcohol.

But now, just ahead of Wednesday’s national legislative elections, polls and analysts suggest that Islamic-based parties are poised for what could be their worst showing since Indonesia’s democratic era began in 1999. At least two of the parties are polling so low that they might lose any presence in the House of Representatives.

“You’re looking at a substantial drop for them,” said Paul Rowland, a Jakarta-based political consultant. “They are not a significant factor.”

The slide in popularity, first noticed in the 2009 elections, appears to be worsening despite studies showing that Indonesians are becoming more pious.