Senate Democrats yesterday brushed off a Republican bid to involve them in deficit-reduction talks, saying that President Reagan must first "get out there and lead" on the issue.

Responding to an overture late last week from Senate Majority Leader Robert J. Dole (R-Kan.), Minority Leader Robert C. Byrd (D-W.Va.) indicated that Democrats were reluctant to join in spending-cuts negotiations until Reagan and the Republicans reached agreement.

"The president's budget is dead," Byrd said. "The Republicans themselves knew that when they saw it. But they don't appear to be making any headway in reaching agreement in their negotiations with the White House.

"We Democrats have not seen their budget; I don't think they have one yet," he added. "Until there is a budget that we Democrats see and examine, we don't know what approaches will need to be taken."

Byrd also indicated reluctance to join in the kind of behind-the-scenes negotiations under way between Republicans and White House officials, saying, "Let us see it and work our will on the [Senate] floor."

But he did not rule out the possibility of bipartisan talks and said that Democratic participation could be discussed at a luncheon caucus of Democratic senators today.

Senate Republicans met for about three hours with White House officials yesterday, reporting afterward that they had made some progress but were considerably short of an agreement. Asked if they were close to agreement, Budget Committee Chairman Pete V. Dominici (R-N.M.) said, "No."

Among the stumbling blocks was agriculture, with the administration insisting on much bigger spending reductions than the senators want. Several participants indicated they hoped to reach an agreement, or possibly an understanding short of agreement, that would enable the Senate to move ahead on deficit reductions by the end of the week.

Although Dole has talked for weeks of including Democrats in the quest for spending cuts, his invitation to Byrd last week was understood to be his first direct overture. Some Democrats interpreted it as indicating a lack of progress in the talks between the White House and Republican senators.

From the start, Democrats have distanced themselves from the deficit-reduction drive, insisting that Reagan should take the lead and expressing fear they will be blamed for unpopular spending cuts if they move out ahead of the president.

As talks continued between Senate Republican leaders and key White House officials yesterday, the White House appeared to be floating a trial balloon about a defense spending compromise under which Reagan might agree to limit the increase for next year to about 3 percent.

Reagan proposed an after-inflation increase of 5.9 percent in his fiscal 1986 budget. The Senate Budget Committee has proposed no growth in the defense budget beyond what is necessary to cover inflation, estimated at between 3 and 4 percent for next year.

White House chief of staff Donald T. Regan was reported to be discussing a compromise at 3 percent, and presidential spokesman Larry Speakes did not deny that it was an option. But Dole and other Senate sources close to the negotiations said it had not been broached before being reported in newspapers.

Meanwhile, two House Democrats proposed a minimum tax of 25 percent for individuals and corporations with taxable incomes exceeding $100,000 a year. Reps. Charles E. Schumer (D-N.Y.), a member of the House Budget Committee, and Marty Russo (D-Ill.), a member of the Ways and Means Committee, said their proposal would raise about $15 billion a year.