"The biggest single issue in America today is the federal deficit," says Robert J. Dole (Kan.), the Senate minority leader and Republican presidential candidate. "In the Dole administration that's the first thing we're going to deal with."

"I want to be the president that with finality does something about the budget deficit that is mortgaging your future," says George Bush, the vice president and Republican presidential candidate.

The Strategic Defense Initiative (SDI), President Reagan's proposed missile-defense system, should not be deployed right away, Dole says. "We ought to continue to develop it, test it, and then when there is something to deploy, we'll deploy. There isn't anything to deploy now, as far as I know."

Says Bush: "We're a long way from getting it developed. I don't want to see a partial deployment. I don't want to see a deployment of part of the system, premature deployment that will compel the Soviets to overwhelm that early deployment."

If the voters in Iowa and New Hampshire think they are hearing rhetorical echoes in the Republican campaign speeches these days, they are right. Less than a month before the first voting, the party's two front-runners, Bush and Dole, sometimes sound as if they were on the same ticket. Veterans of more than two decades in Republican politics and government service, the two agree on virtually all the major issues of the day despite their sometimes rancorous sniping played out on the network news and the front pages.

The two, in effect, are bidding for essentially the same group of voters, and they have been experimenting almost daily in efforts to draw sharper distinctions between themselves. Sometimes the distinctions are difficult to find. For example, Bush cites the Joint Chiefs of Staff as his authority on why SDI should not be deployed right away; Dole cites the Pentagon's SDI director, Lt. Gen. James Abrahamson.

Together, Bush and Dole command the support of more than 65 percent of all Republicans in national polls. Two-thirds of those who favor Bush would select Dole as their second choice; two-thirds of those who want Dole would opt for Bush as second choice, these surveys suggest.

While they don't like to be labeled, Bush and Dole fit the mold of traditional moderate Republicans who tend to stick to the status quo and eschew calls for evolutionary change. In their stump speeches, they both pay homage to the deficit as their primary economic concern, they both express skepticism about Soviet intentions but are supporting the Intermediate-Range Nuclear Forces (INF) Treaty, they both are talking about some modest new domestic spending programs after the severe cuts of the Reagan years.

The other Republicans in the race have sought to challenge Bush and Dole from the right, but, so far, their efforts have failed to slow the moderate front-runners. After seven years of the Reagan presidency, Bush and Dole are saying that the nation needs a slight shift in direction to compensate for unfinished business or neglected programs. Dole focuses on the deficit and programs for the poor; Bush on education and the environment.

But the other Republicans are suggesting that the Reagan "revolution" did not go far enough. For example, the leader among the others, Rep. Jack Kemp (R-N.Y.), has advocated a "phased early deployment" of SDI, opposed the new arms-reduction treaty and denounced the focus of Bush and Dole on budget deficits.

Political scientist Norman Ornstein said Republicans this year face a choice between "continuity and change," and Bush and Dole represent continuity of the final, more traditionally Republican years of the Reagan era. Ornstein recalled a similar choice in 1960 when then-Vice President Richard M. Nixon was the candidate of "continuity" and became the Republican Party's nominee.

"This time it sure looks like the Republicans are going to opt for continuity," Ornstein said. "You've got two candidates who represent continuity" in Bush and Dole, he added, who are engaged in "an increasingly bitter fight over styles, personal qualities, leadership abilities."

The candidates are engaged in a "struggle over the soul and future of the Republican Party," Kemp said. The front-runners are "conventional old-guard Republicans and have never represented the growth and opportunity wing of the party," he added.

Robert Teeter, the Republican pollster who is advising Bush, said the GOP electorate as a whole never became sharply conservative, despite Reagan's dominance in recent years. "The Republican Party is a center-right party, not a right-wing party," he said. Teeter said it remains dominated by what he called "regular" or mainstream Republicans who are conservative on economic issues and foreign policy, but were less so on social issues and who, for example, backed the civil rights efforts of the 1960s.

This segment of voters comprises more than half of the GOP, he said, and Reagan expanded the party with other groups, such as white southerners, blue-collar and Roman Catholic voters.

Teeter said the two front-runners are struggling over the first group of traditional Republicans. "You couldn't run a guy who said 'moderate' on his badge, but Republicans are not going to nominate the most conservative guy in this race," he said.

The Bush-Dole contest may yet be transformed by former television evangelist Pat Robertson or by Kemp, but for the time being the front-runners are pelting each other with like-minded thinking. It is not uncommon for both Bush and Dole to tell audiences they had breakfast with Soviet leader Mikhail Gorbachev last month during the summit. Despite the changes the Soviet leader has made, Bush said, Gorbachev remains a "committed, orthodox Marxist." Dole says Gorbachev is "still a hard-as-nails communist."

Dole said Nicaraguan President Daniel Ortega hasn't changed his basic philosophy, despite the recent lifting of the state of emergency there. "I don't think the record is very good on any Marxist communist giving up power," he says. Said Bush: "We know from history that dictators do not experience sudden conversions in the night. Despots never give up power voluntarily."

Because they are asking voters to chose between them, the two candidates have highlighted the few policy differences they seem to have. Dole said he would be more aggressive in enforcing "linkage" among various areas of U.S.-Soviet relations; Bush does not like the concept. While Dole has said he could support an oil import fee to reduce the deficit, Bush has rejected it.

But on major policy issues it is hard to find a difference between them. Both have identified the deficit as their top domestic concern and both have called for a line-item veto authority for the president to deal with it.

But on the larger choices, Bush and Dole have yet to say how they would reconcile conflicting goals articulated in their speeches.

Bush has vowed not to raise taxes, to increase defense spending and to balance the budget in five years, but also has outlined areas of new domestic spending, including education, the environment and space. When asked about how he would reduce spending, he invariably says Congress is to blame.

Dole has called for some type of across-the-board spending freeze, but also says that low-income programs would be exempt. Asked what he specifically would exempt, Dole has mentioned food stamps, low-income Social Security recipients, the Womens', Infants and Children (WIC) feeding program, and others. But he also has refused to be too specific.

"Well, you want me to be the legislator instead of the presidential candidate," he said. "I'm trying to move out of being the legislator."

"My concept is reduced spending," Dole said. "We'll dot the 'i's and cross the 't's in due time."

Unhampered by issues, the two now engage in an extended quibble over style and character and whose experience counts: "If he can prove he's poor, ever been poor, then he ought to be president," Dole says. "I'm not sure that being in Congress all your life is a part of the answer, I think it may be part of the problem," Bush says.

"I'd like to nail on the wall . . . the Bob Dole record and the George Bush record. It wouldn't take you long to read one of them," Dole says.

"We're running for president. That's an executive branch job," Bush says.