WASHINGTON (AP) -- Republican Sen. James Jeffords of Vermont has told Democrats he intends to abandon his party and become an independent, officials said Wednesday, a switch that would end GOP control of the Senate and crimp President Bush's ability to pass his agenda.

"He's going to leave, that's all I've been told," said one Democratic senator, speaking on condition of anonymity.

A second Democratic senator, also speaking on condition of anonymity, said party leaders had told him Jeffords would align himself with Democrats for organizational purposes, thereby giving them control on a Senate now split 50-50.

Jeffords, a moderate in a party of conservatives, told reporters he would disclose his decision at mid-afternoon.

Several sources, speaking on condition of anonymity, said Jeffords might defer the effective date of his switch until early June. That would enable Republicans to push through Bush's income tax cut, now pending on the Senate floor.

In an atmosphere of extraordinary suspense, Democrats also acknowledged they were concerned about Republican attempts to counter Jeffords' presumed defection by enlisting Sen. Zell Miller, D-Ga., to switch to the GOP.

Officials at the White House said they were in the dark about Jeffords' plans. Vice President Dick Cheney and President Bush met separately with the Vermont lawmaker on Tuesday in an attempt to keep him in the GOP fold. The senator offered no assurances, according to several officials familiar with the private conversations, only promising to give the president a courtesy call.

Rep. Amo Houghton of New York, another moderate Republican in Congress, walked into Jefford's office Wednesday. "It's awful," he said to reporters, shaking his head.

A switch would give Democrats a majority in the Senate for the first time since they lost it in the 1994 elections, elevating Sen. Tom Daschle, D-S.D., to the post of majority leader with the ability to bring bills to the floor. Democrats would take over as chairmen of most committees.

Democrats have quietly courted Jeffords in recent weeks, offering him the chairmanship of the Environment and Public Works Committee if he bolts the GOP, according to sources familiar with the discussions, as well as retention of his seat on the tax-writing Senate Finance Committee.

Stung by the potential defection, the White House urgently contacted longtime Jeffords' donors and political supporters Tuesday, hoping they could persuade the senator to stay in the GOP. Officials also said they were redoubling their efforts to persuade Democratic Sen. Zell Miller of Georgia to become a Republican, in hopes of countering any move by Jeffords.

Apart from its impact on the Senate and the administration's legislative fortunes, a switch could open the door to upheaval within the ranks of Republicans, where the party's leader, Sen. Trent Lott of Mississippi, could face a challenge for his post.

While Jeffords was noncommittal about his plans, a sort of gallows humor pervaded the ranks of Republicans, who hold control in a Senate split between 50 Republicans and 50 Democrats by virtue of Cheney's ability to cast tie-breaking votes.

Republicans who now preside at committee meetings openly addressed Democrats as "Mr. Chairman."

One chairman, Sen. Charles Grassley of Iowa, said he didn't know if Jeffords would switch. Asked if he felt let down, he said he wasn't. "The only thing surprising is how it happened. We always figured it might happen some other way," he said in an apparent reference to 98-year-old Sen. Strom Thurmond of South Carolina, whose advanced age and unsteady step are a constant reminder to Republicans of the fragility of their majority.

Jeffords is among a dwindling band of moderate Republicans in an increasingly conservative party.

House Democratic Leader Dick Gephardt of Missouri said the reported switch was sorry evidence that "there's no room for moderates within today's inside-the-beltway Republican Party."

The chairman of the Education and Labor Committee by virtue of his seniority, Jeffords has a moderate-to-liberal voting record and frequently crosses party lines on high-profile issues. He supports abortion rights, for example, votes for environmental legislation his GOP colleagues generally oppose and favors more education spending than many other Republicans, including Bush.

His relations with the White House have been strained in recent weeks, fallout from a struggle over the budget and the senator's desire for more education funding than the administration wants.

Jeffords sought a commitment from the White House for more federal education funding for disabled students as a condition for supporting the president's spending plan and $1.6 trillion tax cut. The White House balked, and GOP aides accused Jeffords at the time of reneging on a compromise hashed out with Cheney and senior Republican leaders.

Shortly after the vote, Jeffords was not invited to the White House for a National Teacher of the Year award ceremony honoring a Vermont high school educator. In addition, some GOP aides have whispered that the White House might retaliate by seeking changes in a dairy support system that benefits farmers in Vermont and the Northeast.

In addition to Daschle's ascension, Sen. Edward M. Kennedy of Massachusetts would soon replace Jeffords as chairman of the Education Committee, his ability to advance minimum wage and a patients bill of rights bill enhanced. Sen. Patrick Leahy of Vermont would become chairman of the Judiciary Committee, with sway over Bush's judicial nominations.

Sen. Harry Reid, D-Nev., ordinarily would be in line to take over as chairman of the environment committee. But he could defer to Jeffords while retaining his post as majority whip. He declined comment.