Key Senate Republican leaders yesterday urged President Bush to call a special session of Congress to approve his plans for major new military deployments in the Persian Gulf region, drawing a cool response from the White House and top Democratic congressional leaders.

Amid expressions of mounting concern that the United States is moving toward war just as support for its gulf policy is eroding at home and abroad, Senate Democrats also announced that hearings will be held during Congress's mid-winter recess on the administration's move toward a more offensive military posture in the gulf.

At the same time, Secretary of State James A. Baker III defended the continued U.S. military buildup, asserting that Iraq's occupation of Kuwait threatens the "economic lifeline" of the West and that the massive military deployment in the region is justified to protect American jobs. {Details on Page A25.}

In a joint statement, Senate Majority Leader George J. Mitchell (D-Maine), Armed Services Committee Chairman Sam Nunn (D-Ga.) and Foreign Relations Committee Chairman Claiborne Pell (D-R.I.) said the two panels intend to explore "our goals in the region, the potential costs of achieving those goals and the purposes we intend to achieve."

"If it is the president's intention to ask the American people to stand behind a military mission that goes beyond deterring Iraq from attack on Saudi Arabia, the president owes the American people the fullest possible explanation of what our military mission is in that region and how he hopes to achieve that goal," they said.

Nunn said he expects the hearings to start in the next few weeks.

In their appeal for a special session, Senate Minority Leader Robert J. Dole (R-Kan.) and Sen. Richard G. Lugar (R-Ind.), an influential member of the Foreign Relations Committee, said congressional debate could strengthen Bush's hand in dealing with Iraqi President Saddam Hussein.

"The clarity and certainty of our American voice is the primary reason that Iraq may leave Kuwait without military confrontation and that American leadership in this crisis will be taken much more seriously by potentially wavering allies," said Lugar.

But at the White House, press secretary Marlin Fitzwater said the proposal was "unnecessary" because it presupposes "a war that might not occur." At this point, Fitzwater added, "There is no war."

Fitzwater emphasized repeatedly that the massive new troop deployment announced last week was not a step closer to war but part of a process to put more pressure on Iraqi President Saddam Hussein to withdraw. "We continue to rely on the economic sanctions and on the military pressure of our presence there as the principal weapons for convincing Saddam Hussein to leave Kuwait," he said.

Although some lawmakers such Sen. Edward M. Kennedy (D-Mass.) said they would welcome a special session as an opportunity for Congress to go on record against offensive military action in the gulf, other Democratic leaders appeared to have reservations of varying intensity about the idea.

As long as Bush is using the deployment of 200,000 additional U.S. troops as a threat to persuade Iraq to withdraw from Kuwait, congressional approval is not required, Mitchell said in response to questions about the Republicans' proposal.

"No one wants a session of Congress with no clearly defined purpose," he added, although he said he would consider any proposals for a special session.

But if Bush decides to go to war, the Constitution provides in "clear, explicit and unmistakable" terms that the president must get prior approval from Congress before he acts, Mitchell said. "Our firm view is that the president has no legal authority, none whatsoever, to commit American troops to war in the Persian Gulf or anywhere else" without congressional authorization.

House Speaker Thomas S. Foley (D-Wash.) was also described by an aide as reluctant to call for a special session unless Bush changes his gulf policy.

House Armed Services Committee Chairman Les Aspin (D-Wis.) agreed with Foley and Mitchell, saying, "You can't have a productive discussion about a hypothetical."

Responding to Lugar's proposal that Congress debate and approve a specific authorization for administration policy in the gulf crisis, Nunn said he thought Lugar was "right on the basic principle" that Congress should act before any military action is taken.

"But the prerequisite ought to be that the president decides it is in our vital national interest to liberate Kuwait and that the embargo {against Iraq} is not working and that the {military} buildup can be sustained," Nunn said.

As for his own position, Nunn said, "I like the policy we had before," describing it as one aimed at deterring further aggression by Iraq, protecting Saudi Arabia and giving the embargo time to work. "We ought to be taking the position that the policy is working," he added.

Other Democrats also were skeptical. "If the president is proposing that we give him a blank check, I suspect he'll run into trouble," said Sen. J. James Exon (D-Neb.), a senior member of the Armed Services Committee. Sen. Lloyd Bentsen (D-Tex.) said he thought it would be a "serious mistake" if a special session wound up giving Bush a "blank check" in the gulf.

But Sen. John W. Warner (R-Va.), ranking minority member of the Armed Services Committee, said "there is a definite groundswell" in Congress for a special session to deal with gulf policy.

Neither Dole nor Lugar called for a formal declaration of war, although Lugar said the congressional authorization he envisioned would amount "in effect" to the same thing because the policy could lead to war.

In a reflection of congressional criticism that Bush has failed to articulate fully enough the reasons for the huge troop buildup, Lugar said the president should first state "as clearly as possible specific missions for the United States' military forces and his reasons for employing those forces." Then, he said, Bush and congressional leaders should call Congress to Washington to debate and vote whether to authorize whatever is necessary for "complete fulfillment" of those missions.

If Congress were to refuse to authorize the president's plan, Lugar said, it would be "tragic" but "it is better to know that now" than after American lives are put at risk, he said.

Noting reservations among allies and polls indicating that American public support for the president's handling of the gulf crisis is declining, Lugar said, "This is the time to stop the erosion. We cannot have an unraveling at this point."

"I think it ought to be put up to the Congress: put up or shut up," Dole said in an interview with the Associated Press. "And, if they say no, well then, they say no. And then the president has to decide whether to go it alone." Later, Dole indicated he agreed with Mitchell that it would be necessary to define in advance what Congress would do if it returns.

"The worst thing that could happen would be to come back, draft a resolution and have it fail," he said.

Dole discussed the proposal for a special, lame-duck session with Bush at lunch at the White House, but said afterward that the issue was not resolved. "We'll have a much better fix when the president returns {from the Middle East at the end of next week} what may or may not happen. . . . I don't think he ruled it out or in."

Normally it is the president who calls Congress back into session after it has adjourned for the year. But this year, with the gulf crisis in mind, Congress acted in its adjournment resolution to empower Mitchell and Foley to call Congress back in case of an emergency.

Bush is scheduled to meet today with the joint congressional leadership, and Baker and Defense Secretary Richard B. Cheney are to give briefings later for all senators. The senators are in town to elect their leaders for the 102nd Congress, which officially convenes Jan. 3.

A senior official said the White House's major reservation about calling a special session now is that the situation "is not ripe yet," and added that over the next few weeks, some additional steps in gulf diplomacy, including a possible United Nations vote on whether to support military action to enforce the economic sanctions against Iraq, are possible. Such a vote would strengthen the administration's hand in arguing for a similar vote in Congress.

One senior official said the White House "brought ourselves some of this turmoil" by failing to consult adequately with Congress before Bush announced the latest deployment. An official acknowledged that Cheney, less than two hours before Bush's news conference last week, began calling Hill leaders but could not locate many of them, and those he did find he gave very little information. Nunn complained that he and other key congressional leaders were not consulted before the deployment was announced.

When Bush meets with the leaders today he will provide "some scene-setting and some context" for the gulf buildup, a White House official said, arguing as Fitzwater did yesterday that the president is not shifting closer to war or radically changing position.

A White House official said that during Bush's luncheon with Dole and House Minority Leader Robert H. Michel (R-Ill.), Dole was asked whether Congress would vote in favor of authorizing or approving offensive military moves in the gulf. "He could not say we would win that vote," the official said, explaining that is one major reason the White House is resisting any special congressional session.

Dole first outlined his idea for a special session in a letter to Bush last Friday but did not make it public until yesterday.

Staff writer Ann Devroy contributed to this report.