WASHINGTON — A top Democratic leader opened the door yesterday to granting American telecommunications companies retroactive legal immunity for helping the government conduct electronic surveillance without court orders, but said the Bush administration must first detail what those companies did.

The House majority leader, Rep. Steny Hoyer, a Democrat of Maryland, said providing the immunity will likely be the price of getting President Bush to sign the legislation extending the government’s surveillance authority. About 40 pending lawsuits name telecommunications companies for alleged violations of wiretapping laws. Democrats introduced a draft version of the law yesterday — without the immunity language. “We have not received documentation as to what in fact was done, for which we’ve been asked to give immunity,” Mr. Hoyer said.

In a conference call with reporters, a senior Justice Department official called Mr. Hoyer’s offer “encouraging” but would not commit to sharing the data. The official spoke only on condition of anonymity while negotiations with Congress continue.

The bill would replace a law enacted in August that is due to expire early next year. That bill was hastily adopted under pressure from the Bush administration, which said changes in technology had resulted in dire gaps in its authority to eavesdrop on terrorists.