As Bob Dole exits the Senate this week, power shifts to a new generation of younger, more aggressively conservative, more ideologically-driven Republican leaders.

At 72, Dole is last top congressional leader in either party of the generation molded by the experiences of World War II and the Great Depression.On Tuesday Dole's GOP colleagues will pay elaborate tribute to him as he departs. The next day, Republicans will elect new leaders to at least three of the top four party posts in the Senate - leaders who represent a marked contrast to Dole in style, outlook, and age.

Dole's expected successor is Sen. Trent Lott of Mississippi, 55, currently the No. 2 GOP leader. Lott has strong backing from the 11 GOP Senate freshmen and other, less senior Republicans who have been critical of many of the Senate's hidebound ways.

Dole's departure and Lott's succession will close out an era in the Senate marked by an exaggerated deference to seniority, where the majority leader and a few powerful committee chairmen could set the agenda.

Under Lott, GOP senators who wish to retain their committee chairmanships and other privileges are more likely to be required to toe the party line on key votes or suffer the consequences.

Younger conservatives say they don't want to see a repeat of last year's experience with the balanced budget constitutional amendment, which failed by one vote. Senate Appropriations Committee Chairman Mark Hatfield of Oregon was the only Republican to vote against the amendment, but he was not punished by Dole.

Lott is also more likely than Dole to seek opportunities to challenge Democrats who try to use Senate rules to hold up legislation in order to stymie the GOP agenda.

"I think he's going to be a little more willing to press the Democrats into a corner," said Dave Mason, a congressional expert with the conservative Heritage Foundation. "Dole had to be careful about appearing to be ineffective or harsh."

Lott is being challenged for the position of GOP leader by his Mississippi colleague, Thad Cochran, currently the No. 3 Republican leader. While equally as conservative as Lott, Cochran's support is based primarily in the Senate's dwindling old guard. They prefer his quiet gentility to Lott's hard-edged rhetoric.

Cochran, 58, also appeals to moderates, who view him as more willing to compromise with senators uncomfortable with demands by the GOP's hard right for deep cuts in both taxes and social programs.

The numbers, however, are with Lott. Of the 53 Republicans in the Senate, Lott says he has commitments from 28 - enough to win the race. In addition to the freshmen, Lott has the support of more than a dozen Republicans who served with him previously in the House. Cochran has said he may pull out of the contest just before Wednesday's vote if it's clear Lott will win.

Lott served as the No. 2 GOP leader in the more tumultuous House until his election to the Senate in 1988. There, he forged close relations during the early 1980s with then-GOP backbenchers Newt Gingrich, Dick Armey and other conservatives who advocated a more confrontational strategy in dealing with Democrats.

Those Lott allies helped engineer the political revolution that culminated in 1994 with the GOP taking control of the House for the first time in 40 years. Gingrich has called Lott "a mentor."

Moderates warn that with the GOP's thin majority in the Senate, Lott can't afford to take them for granted.

"He's got to tread very carefully to start with to build up everybody's confidence," said Sen. John Chafee, R-R.I.

However, many GOP moderates are retiring at the end of this year - including Sens. Nancy Kassebaum of Kansas, Bill Cohen of Maine and Hatfield.

Lott's allies say he's enough of a pragmatist not to alienate moderates while attempting at the same time to induce a greater degree of party discipline.

"Trent Lott knows one thing as leader - you've got to have to the votes," said Sen. Larry Craig, R-Idaho, who served in the House with Lott.

"He also understands the character of the Senate ... where each senator has tremendous individual power," said Craig, 51.

Senate Democratic leader Tom Daschle of South Dakota, who also served with Lott in the House, said he hopes Lott will attempt to set aside the partisanship and election-year politicking that has marked the Senate agenda this year in an effort to break to the impasse over health care, welfare and minimum wage legislation.

"To the degree we can work together, a lot will get done," Daschle said. "To the degree that there is no cooperation, I can tell you very little will get done."

Daschle also warned Lott against trying to muscle legislation through over Democrats' objections.

"You need 60 votes to be a boss around here," Daschle said, a reference to a Senate rule requiring 60 votes to shut off debate.

Replacing Lott as the No. 2 GOP leader will be Sen. Don Nickles, 48, of Oklahoma, who is unopposed for the post. One of the Senate's most passionate abortion opponents, Nickles has strong ties to the party's conservative Christian wing.

In the three-way race for chairmanship of the Republican Policy Committee, Craig is believed to have the edge. A member of the National Rifle Association's board of directors, Craig has reflected the populist strain among many Western Republicans who advocate reducing the size and influence of the federal government, tranfering federal lands to private ownership and restraining environmental regulation.

If he doesn't succeed in his bid to become Republican leader, Cochran plans to retain his position as GOP conference chairman through November, after which he will step down. Sen. Connie Mack of Florida has said he will seek the position at that time.