WASHINGTON, July 23 — Democratic lawmakers slowed business in the House to a crawl today, conducting an hour or two of obstruction to protest the refusal of House Republican leaders to expand the child tax credit for low-income families.

Using one of the few tools available to members of the minority party, Democrats repeatedly forced the House to stop debate and vote on procedural motions they knew would not pass, like immediate adjournment. House Democrats said they also planned to force a vote every half hour on Thursday to make the same point.

"Democrats are in the heat of battle on the floor of the House using every weapon in our arsenal to disrupt the schedule and to force a vote on the child tax credit," the party's House leader, Representative Nancy Pelosi of California, said.

Beginning Friday, the government will mail checks of $400 per child to 25 million middle-income families, as part of President Bush's new tax cut law. But 6.5 million minimum-wage families with children will not receive the checks, the result of a decision in May by the White House and Republican lawmakers not to include them in the tax cut because most do not pay federal income taxes.

House Republican leaders have said they will increase the tax credit for low-income families only as part of a much broader tax-cut package for wealthier families, a position that has led to a stalemate in talks with less conservative Senate Republicans. Today's slowdown was the latest effort in a seven-week barrage of news conferences and demonstrations by Democrats to make Republicans pay a political price for their position.

The effect of the slowdown, however, was mostly to annoy Republican appropriations leaders, who had to stay much later than planned to pass an unrelated foreign operations spending bill tonight.

"This really throws us behind," said Representative C. W. Bill Young, the Florida Republican who is chairman of the Appropriations Committee. "I would really like to get this bill done, but they're using one of the tools of the minority."