House GOP leaders plan to offer a tax break to help seniors buy prescription drugs, part of an effort to blunt President Clinton's recent initiative on the politically potent issue, lawmakers said yesterday.

The proposal to allow seniors to claim a tax deduction for buying medicines will be part of an $864 billion tax-cutting bill under consideration in the House. The Ways and Means Committee last night began work on the bill, which also calls for a 10 percent across-the-board reduction in income tax rates and a substantial break on capital gains.

Even as House Republicans moved quickly on taxes, they found themselves facing roadblocks to the left and the right as they resumed work on key spending bills. Democrats tried unsuccessfully to attach gun control measures to a treasury-postal appropriations bill, while GOP conservatives continued to press for even deeper cuts in spending than contemplated by House appropriators.

Fiscal matters are at the top of the congressional agenda this week, as lawmakers consider how to divvy up budget surpluses that could total nearly $3 trillion over the next decade.

Ways and Means Chairman Bill Archer (Tex.), author of the GOP tax bill, said the surplus is large enough for a hefty tax cut while also safeguarding Social Security and revamping the Medicare health program for the elderly. "What this debate is about is downsizing the power of government and upsizing the power of people," Archer said.

But Clinton and congressional Democrats ratcheted up their criticism of GOP tax-cutting proposals, complaining that they are far too big and threatened prospects for a comprehensive budget and tax compromise this fall.

During a speech in Miami, Clinton said it would be a mistake to divert too much for a tax cut before Social Security and Medicare are fixed, including a new prescription drug benefit for Medicare recipients. The president also said such a large tax cut would threaten future spending on key programs.

"So I ask again the Republican leaders in Congress, for the sake of saving Medicare and strengthening our future, to reduce the size of your tax cut and join us in putting first things first," the president said.

While spurning his demand for a smaller tax cut, GOP lawmakers appeared anxious to match Clinton's desire to provide new help for Medicare recipients to buy prescription drugs. Clinton's plan would charge patients a monthly premium in exchange for the government picking up half the cost of medications up to a certain limit.

The House GOP now appears to be pursuing a different approach to the same problem. Speaker J. Dennis Hastert (R-Ill.) met with key lawmakers yesterday to draft a plan under which those seniors without prescription drug coverage could claim a tax deduction for the cost of buying such coverage. Lawmakers said they will offer a plan later for direct financial assistance for those seniors living near or below the poverty line.

"The reason is we as Republicans want to help people with the cost of these pharmaceuticals, but at the same time we don't want to break the bank with Medicare, which is already hemorrhaging money," said Commerce Committee Chairman Thomas J. Bliley Jr. (R-Va.).

Rep. Jim McCrery (R-La.) said the new deduction would not add to government costs because it would be contingent on cost savings envisioned by a Medicare panel chaired by Sen. John Breaux (D-La.) and Rep. Bill Thomas (R-Calif.).

Meanwhile, lawmakers continued to work on shepherding fiscally conservative bills. Determined to pass the 13 annual appropriations bills by the August recess, top Republicans have outlined a grueling schedule over the next few weeks.

As the House Appropriations Committee considered the $13.5 billion treasury-postal bill yesterday, a compromise quickly fell apart as lawmakers fought over a spending cut and gun control measures.

Rep. Steny H. Hoyer (D-Md.), the ranking member on the treasury-postal subcommittee, warned that Democrats might defect once the panel's chairman, Jim Kolbe (R-Ariz.), offered an amendment to cut $240 million from the Internal Revenue Service's restructuring efforts and Year 2000 computer preparations.

The debate became substantially more heated, however, when Democrats offered a trio of gun control amendments modeled on the measures adopted by the Senate in June, including a plan for three-day background checks at gun shows, banning the importation of large-capacity ammunition clips and requiring the sale of child-safety locks along with handguns.

Kolbe said that he and many of the Republicans supported some of the gun measures, but it was inappropriate to add those provisions to the spending bill.

Democrats argued that they were compelled to press the subject because House and Senate leaders have failed so far to appoint negotiators on the juvenile justice bill, which contains the Senate's gun language. But House Majority Whip Tom DeLay (R-Tex.) responded that leaders would appoint negotiators on the juvenile justice bill by the end of the week.

Staff writer Sue Anne Pressley in Miami contributed to this report.