The Bush administration sent a letter to House and Senate leaders Tuesday that included the threat of a presidential veto of this year's supplemental budget if it is more than the $27.1 billion that President Bush has requested.

"The administration strongly opposes this bill and also would strongly oppose any amendment to further increase spending above the president's request," the "Statement of Administration Policy" written by White House budget director Mitch Daniels read.  If the bill "were presented to the president in its current form, his senior advisers would recommend that he veto the bill."

Supplemental appropriations generally include emergency spending that was not planned for in the current fiscal year. This year, the supplemental was written predominantly to fund homeland defense and the war on terror, but critics say lawmakers are packing it with pork.

A Bush administration official said this could be the biggest partisan budget skirmish yet.

The $29 billion House supplemental bill passed on a late night 280-138 vote one day before the Memorial Day break. The Senate began debating its $31.4 billion version on Monday.  On Tuesday, it passed by 91-4 a provision to drop proposed restrictions on emergency airline loans.  Sen. Robert Byrd, D-W. Va., wanted to limit the loans as a means of holding down the cost of counterterrorism legislation.

The alleged pork includes money to raise honeybees and better fund the Humane Society, as well as add $5 million for Alaskan fishermen who are suffering through a bad halibut season, among other non-defense related measures.

Prior to the holiday recess, Sen. John McCain, R-Ariz., and others complained that the Senate Appropriations Committee, led by Byrd was trying to slip the bill through the Senate quickly so that senators couldn't dwell on the pork issues.

"The appropriators are going to understand that there are other senators who need to be involved when in an emergency supplemental appropriations bill, there are policy changes which have nothing to do with any national emergency," McCain said during a floor debate last month. 

On Monday, Byrd said that the president's proposed $27 billion plan under-funds the effort to combat bioterrorism and bolster security at nuclear facilities, water systems and other areas.

"We know where those gaps are," Byrd said. "And if we know where those gaps are, you can be sure that the terrorists know."

Tom Schatz, president of Citizens Against Government Waste, said he thought the president's veto threat is "great."

"I think it's about time that someone did this during the process. There are some people who take the war on terrorism seriously and understand we have to reallocate resources and most of those people are at 1600 Pennsylvania Avenue, the other people around the block, really don't get it yet," Schatz said, referring to the White House address. 

Among the additions in the supplemental bill are provisions for the National Oceanic and Atmospheric Administration; $2.5 million for a coral reef program to conduct coral mapping in the waters of the Hawaiian islands; and $2 million for the planning and design of a storage facility to be located in Suitland, Md., and used for long-term storage of the Smithsonian's collections of preserved animal species.

Votes will also be taken to determine whether to give money to the U.S. Geological Survey Earth Resources Observation Systems (EROS) Data Center in Sioux Falls, S.D., for a date processing and backup system for satellite and other remotely sensed data. The proposed funding does not relate to the war on terrorism or homeland security. EROS is considered a mission critical site for the Department of the Interior, but it is not considered to be an element of critical infrastructure of national importance.

The bill also provides $55 million for a grant from the Federal Railroad Administration to the National Railroad Passenger Corporation, in other words, Amtrak. The Senate supplemental bill provides $20 million to repair damaged Amtrak equipment, $12 million for Amtrak security and $23 million to do a heavy overhaul of the corporation's rail fleet. Two of the earmarked projects in the Senate bill are for routine fleet repair and overhaul and are not related to the war on terror or homeland security.

Amtrak has not demonstrated emergency safety or security needs for the projects earmarked by the Senate. However, the corporation overall is in a dire financial situation and there is a danger that it may need additional federal subsidies larger than the $521 million appropriated in fiscal year 2002 to survive this year.

Democrats were upset at a House vote to include in the supplemental a provision to raise the debt limit $750 billion to prevent a U.S. loan default that Democrats say could have been avoided if there had been no tax cut last year. Republicans say the war on terror and supplemental spending as well as last year's recession contributed to U.S. borrowing.

Fox News' Kelley Beaucar Vlahos contributed to this report.

Carl Cameron currently serves as Fox News Channel's (FNC) Washington-based chief political correspondent. He joined FNC in 1996 as a correspondent.