Worried that congressional proposals for huge tax cuts could jeopardize increases in defense spending, the Pentagon has appealed to the White House to hold the line against deep tax breaks or risk gutting military modernization programs.

The military brass appears to be nervous about the outcome of negotiations between President Clinton and leading Republican lawmakers over how to spend the federal budget surplus, now estimated at about $1 trillion over the coming decade.

But senior Republican aides yesterday dismissed the Pentagon's jitters as unfounded, asserting that the GOP remains strongly committed to higher defense spending. They said the Pentagon's decision to publicize its concern -- with apparent approval from the White House -- was little more than a ploy to strengthen Clinton's hand in the coming budget talks.

Republicans are pushing various tax cut proposals with totals ranging from $775 billion to $864 billion over 10 years. The administration favors a more modest $250 billion in tax reductions, with most of the surplus going for improvements in Social Security, Medicare and education programs as well as defense.

Clinton has invited Republican leaders to come to the White House on Monday to discuss their differences in the first such get-together since the White House substantially raised its budget surplus forecasts two weeks ago. Saying they fear the talks could produce a compromise shortchanging future military spending, two senior defense officials called in a reporter to make known that they had pressed top Clinton aides not to sell out the Pentagon.

"We're putting a marker down with the White House," one of the officials said. "We told them: Don't close out this deal and leave us behind."

Confronted by warnings from the military chiefs of a serious erosion in defense equipment and troop morale, Clinton promised late last year to dip into the projected federal surplus and give the Pentagon an extra $127 billion through 2009 -- the largest sustained rise in defense spending since Ronald Reagan was president.

A tax cut of the magnitude being proposed by the Republicans would effectively wipe out this increase -- and more, defense officials said. It would result in a loss of $198 billion in projected defense spending between 2005 and 2009, the officials said. That calculation is based on the difference between the administration's long-term spending plan and the latest congressional budget resolution.

The loss of so much funding, at a time when the Pentagon expects to be paying heavily for a new generation of fighter jets and ships, would compel either a sharp reduction in troop levels or the cancellation of some major modernization programs, the officials said.

But congressional Republicans contend that a big tax cut and higher defense spending are not mutually exclusive. And they intend to pursue both.

"We have a requirement to get the tax overpayments coming into this town out of town, but only after we address the national security issue," said John Czwartacki, spokesman for Senate Majority Leader Trent Lott (R-Miss.).

In recent months, congressional Republicans have sought to outbid the administration's own military spending surge. Congressional committees added from $5 billion to $8 billion to the administration's proposed $281 billion defense budget for fiscal 2000, which itself represents an inflation-adjusted increase of about $12 billion over what the administration had planned just a year earlier.

Lawmakers also responded to NATO's air campaign against Yugoslavia with a nearly $11 billion emergency spending bill, almost double the $6 billion that Clinton requested.