Washington ? Republican divisions in the Senate could complicate efforts to extend three of President Bush’s most popular tax cuts this week. If allowed to expire, Americans could pay $50 more in taxes — and lose up to $300 in tax benefits for each child — next year.

A group of the Senate’s Republican and Democratic moderates on Monday asked GOP leaders to consider the growing federal deficit as they work to safeguard the tax cuts.

“The last thing our hard working American families expect is a higher tax bill next year,” said Sen. Max Baucus of Montana, ranking Democrat on the Senate Finance Committee. “Our bipartisan proposal is a roadmap to cut taxes without adding to our deficit woes.”

Divisions among Senate Republicans thwarted efforts this year to write a budget outlining spending and tax policies for 2005 because they didn’t put limits on future tax cuts. Republicans control the Senate by very few votes, enabling moderates to exert a strong influence on tax and spending policies.

Several of those moderates want to see the three popular tax cuts locked in for one more year and its roughly $30 billion cost be paid for by closing tax shelters and loopholes and retaining customs service fees.

If the tax cuts expire at the end of the year as scheduled, Americans can expect tax increases in three forms. The child tax credit would drop from $1,000 to $700. The bottom 10 percent tax bracket would shrink, increasing taxes on about $1,000 in income from 10 percent to 15 percent. And married couples who had enjoyed benefits from an increased standard deduction and wider tax brackets would see some of those benefits disappear.

A spokeswoman for Senate Finance Committee Chairman Charles Grassley, R-Iowa, said his top priority is to fashion a bill that can pass the House and Senate and become law to prevent those tax hikes from happening.

Preserving the tax cuts for five years would cost about $120 billion.