By Patricia Zengerle

WASHINGTON (Reuters) -U.S. senators from both parties voiced doubts on Tuesday about House Republicans' plan to provide $14.3 billion in aid to Israel by cutting Internal Revenue Service funding, without providing aid to Ukraine, and Democratic President Joe Biden threatened to veto the bill were it to pass.

In the first major legislative action under new Speaker Mike Johnson, House of Representatives Republicans unveiled a standalone supplemental spending bill only for Israel on Monday.

This is despite President Joe Biden's request for a $106 billion package that would include aid for Israel and Ukraine and funding to boost competition with China in the Indo-Pacific as well as security along the U.S. border with Mexico.

Republicans have a 221-212 majority in the House, but Biden's fellow Democrats control the Senate 51-49. To become law, the bill would have to pass both the House and Senate and be signed by Biden.

The top Senate Democrat said the Republican bill would be dead on arrival in the upper chamber, even if it passed the House.

"The bottom line is it's not a serious proposal," Senate Democratic Majority Leader, Chuck Schumer, told reporters.

The administration said Biden would veto such a bill were it to reach his desk.

"This bill is bad for Israel, for the Middle East region, and for our own national security," the White House's Office of Management and Budget said.

Senator Mitch McConnell, the Republican leader in the Senate said he felt the four issues needed to be addressed.

"We need to treat all four of these areas, all four of them, Ukraine, Israel, Taiwan and the border," McConnell told reporters.

Secretary of State Antony Blinken met with Johnson on Tuesday after testifying in the Senate. At the hearing, Blinken and Secretary of Defense Lloyd Austin said Ukraine needed continued U.S. assistance to win its fight against Russian invaders.

Blinken told reporters: "It was a very good meeting. I appreciate the opportunity. I'll leave our conversation at that."

State Department spokesperson Matthew Miller said they had discussed issues including Biden's request for support for Ukraine and Israel.

Republicans are expected to pass the legislation in the House as soon as this week.

US House Republicans' Israel-only aid bill opposed in Senate, by Biden