White House looks to Reagan impact in '88. If the President achieves even part of his remaining agenda, officials say, the '88 GOP candidate will not risk distancing himself from the Reagan legacy.

Imagine this scenario: Ronald Reagan concludes an intermediate-range nuclear arms pact with Moscow and plays host for Mikhail Gorbachev's visit to the United States later this year. The two leaders reach agreement on general principles for a strategic nuclear arms agreement and the Soviet leader invites the President to the Soviet Union.

Enter 1988: Mr. Reagan tours the Kremlin, signs an arms framework-style accord with Mr. Gorbachev, and returns home in a blaze of diplomatic glory. By fall - assuming the economy is ticking along - the Democrats are wringing their hands and the Republican candidate for President is elected by a comfortable margin.

Implausible? White House officials shy from any suggestion of such a design. One step at a time, they say. But they maintain that Reagan still has an opportunity to emerge triumphant from the trials of his presidency and provide a solid foundation for the election of another Republican to the Oval Office in 1988.

``People have always tended to downplay this President,'' says a top Reagan aide. ``There's a tendency to read the potential negative side rather than the positive in looking at this presidency.''

To speculate about a Moscow summit is premature, the aide says. ``But we have focused on START [strategic arms reductions talks] as the logical next step,'' he adds. ``Clearly the President would like to build on whatever we accomplish in this round.''

Another key White House official says: ``The administration has emerged from the Iran-contra episode stronger than could have been imagined last January. A lot of people will be surprised by the impact of the President on the legislative calendar.''

The expectation at the White House is that Reagan will ultimately win the fight over the nomination of Robert Bork to the Supreme Court and that, assuming the Shultz-Shevardnadze meetings this week are successful, the chances for a superpower summit meeting this fall are good.

At the same time Reagan aides are careful to play down expectations. ``We're not there yet,'' says the senior official. ``You've got to be prepared that if it doesn't work, you can walk away from it.''

News reports in recent weeks have suggested that the President has lost a degree of sharpness and physical verve. The stories fit in with the general perception that the administration is on the decline, because of the damage done by the Iran-contra scandal, the lack of time left in the administration, and the President's age.

But White House officials insist that the Reagan presidency is not over. The fact that Reagan is concentrating on only a few agenda items - Bork, an INF (intermediate-range nuclear forces) agreement, Central America, and the budget - is in keeping with his traditional practice, they stress.

``He's always worked most effectively with a small menu, focusing on four or five issues,'' says the senior aide. ``He's more effective with an agenda that is clearly definable. ... You have effectiveness in the Cabinet and so he doesn't have to be the only voice.''

``I've never seen him more involved in the process of governing as recently,'' says another White House official. ``This September and October will be the biggest time of his presidency.''

While not underestimating Reagan's difficulties, political observers say the kind of scenario outlined above cannot be entirely dismissed. According to opinion polls, Reagan's job approval rating remains in the vicinity of 50 to 57 percent, which is high by historical standards. Harry Truman's rating fell to the 20s in his penultimate year. Dwight Eisenhower's was in the 50s.

``On the whole Reagan's problem has never been particularly acute with the general public, though Americans do not feel they got the truth on Iran-contra,'' comments Everett Carll Ladd, head of the Roper polling organization. ``His ratings are not perfect but not bad. ... The Republican candidate in '88 should see Reagan as a distinct advantage, even though he has to show how he would differ [in office].''

Reagan's political advisers make this same calculation. ``It's very good to be at this point in the [presidential] cycle,'' says a political adviser. ``That will stand us in good stead in '88.''

White House officials anticipate an increase in revenue this year because of the tax reform, and continued economic expansion in 1988. ``That should have a positive impact on the deficit, putting it on a downward path,'' the aide says. If the economy holds up through '88 without a recession, he adds, ``this will stand the Republicans in good stead.

The President's political aides are still in the process of deciding his election strategy for the rest of the term. But they see the broad goals as twofold: (1)building up a substantive record to shape the '88 political debate and (2)giving Reagan a conspicuous role in campaigning for the GOP nominee. If Reagan is successful in achieving even a part of his remaining agenda, such as approval of the Bork nomination and achievement of an INF agreement, officials say, the Republican candidate will not risk divorcing himself from the Reagan legacy.

``The theme of `peace and prosperity' is a winning combination,'' says the political aide. ``And if we have that next year that will be well received.''

The Iran-contra issue is still seen as a liability, however. White House officials still await the congressional report on the recent hearings and possible legal action by independent counsel Lawrence Walsh. These could generate more political waves, further damaging the President's standing in Congress.