It will be hard to top the color and drama of his fourth U.S.-Soviet summit, but President Reagan's aides and backers say he will have plenty to keep him busy until he leaves office 7{ months from now. There's just a chance that his schedule might include a fifth meeting with Soviet leader Mikhail S. Gorbachev to sign a treaty reducing superpower arsenals of long-range nuclear missiles. ``I think what we are seeing is that Ronald Reagan has not yet reached the peak of his powers or his accomplishments,'' says Martin Anderson, the president's former top domestic policy adviser and author of a book about his administration. Reagan's agenda will include an economic summit meeting with leaders of the industrialized Western democracies and Japan, campaign trips on behalf of George Bush and other Republican candidates and a brief appearance at the GOP convention in New Orleans. He is also expected to squeeze in four more vacation trips to California before he turns over the reins to his successor at noon next Jan. 20. As they have for many months, the president and his aides also say that efforts continue to secure the freedom of nine American hostages held in Lebanon. Administration efforts to force Gen. Manuel Antonio Noriega from power, which collapsed as Reagan was on his way to the summit, may also be resumed. On the president's immediate schedule are a couple of speeches in Washington in which he will report on his Moscow visit. Details of the speeches had not been announced as the president prepared to leave Moscow. Still up in the air was the future of a proposed treaty reducing intercontinental ballistic missile arsenals by 30 to 50 percent, which both sides had originally said they hoped might be signed during the meetings in the Kremlin. ``We are both hopeful that it can be finished before I leave office,'' Reagan told students at Moscow State University. ``But I assure you that if it isn't ... I will have impressed on my successor that we must carry on until it is signed.'' Anderson, interviewed by telephone at the Hoover Institution at Stanford University, where he is a senior fellow, said, ``I would predict that he and General Secretary Gorbachev are going to be working even harder to put together a reduction in the big weapons.'' ``They may not get to the full 50 percent but I wouldn't be surprised if they did get some agreement,'' said Anderson, who in his recent book, ``Revolution,'' depicted nuclear arms reduction as Reagan's overriding concern during his presidency. Gorbachev and Reagan, who first met in Geneva in 1985 and subsequently got together in Reykjavik, Iceland, and in Washington before their session in Moscow, have indicated they would be willing to meet again to sign such a treaty. With difficult negotiations still ahead, no concrete plans have been made, but some sources have suggested Budapest, Hungary, as a possible site. More immediately, Reagan will meet in Toronto June 19-21 with heads of government from Canada, Japan, West Germany, Britain, Italy and France for the 14th annual economic summit. With the exception of Britain's Prime Minister Margaret Thatcher, he will have been in office longer than any of them. ``There are no burning issues,'' said one administration official. ``It's a `where we have been and where we are going' kind of thing.'' Reagan's speech at the Republican National Convention in New Orleans Aug. 15-18 is expected to be a brief drop-in enroute to his annual August vacation at his ranch north of Santa Barbara, Calif. He is also expected to visit the ranch in July and, as usual, spend Thanksgiving there and round out the year at the home of old friend Walter Annenberg in Rancho Mirage, Calif. The president is expected to make campaign appearances on Bush's behalf after the vice president's expected nomination at the convention. ``Nothing has been scheduled, but he will be doing campaigning for the vice president and a lot of campaigning for Senate and House candidates,'' Deputy White House Press Secretarty B.J. Cooper said. It does not sound as dramatic as meeting with refuseniks in Moscow, dueling with Gorbachev inside the Kremlin walls or answering barbed questions from Soviet students. But, as Reagan said in a May 2 speech to the U.S. Chamber of Commerce reviewing his administration's accomplishments, ``We aren't at the end yet.''