HOUSTON, JULY 11 -- The world's major industrialized nations ended their annual economic summit here today with a series of compromise agreements on aid to the Soviet Union, reduction of agricultural trade subsidies and protecting the environment.

The final agreements reflected concessions by all the participants that still left them sharply divided on key issues, which will have to be resolved later. Nevertheless, the three-day summit ended in an upbeat mood. "This was a summit that addressed itself to a rapidly changing world," President Bush said at a closing news conference. "It is no small achievement that we came to a positive and unanimous conclusion on so many important and difficult issues."

Bush, hosting his first economic summit in his adopted home town, appeared to have succeeded in accomplishing what he had wanted.

Responding to a request for economic assistance from Soviet President Mikhail Gorbachev, the leaders agreed to a six-month study of the stumbling Soviet economy, directed by the International Monetary Fund (IMF), and to provide the Soviets with technical assistance. They also endorsed individual aid programs for the Soviets from nations such as West Germany, France and Italy, who want to go ahead now.

But before the other nations at the summit -- the United States, Canada, Great Britain and Japan -- are ready to offer direct financial aid, they demanded evidence that the Soviet Union will pursue further reforms, including reduction of military spending.

In contrast to the NATO summit a week ago, in which leaders sought to assuage Gorbachev's concerns about German unification and the military threat from the West, the message of the economic summit appeared to be part carrot, part stick.

"The response is a positive one," West German Chancellor Helmut Kohl said at a closing news conference. "We all consider it necessary." Bush called the final agreement "an effort to . . . encourage forward motion and be helpful to the Soviet Union in terms of reform." Then he added, "They need much, much more reform."

Bush and Kohl also appeared to differ on what will happen after the study of the Soviet economy is completed at the end of the year, with Kohl suggesting the other nations should be ready to help Gorbachev and Bush continuing to resist. "Mr. Gorbachev understands that at this juncture, sending money from the United States is not in the cards," Bush said, adding that "certain things have to happen" before he will change his mind.

Bush said today he had already sent Gorbachev a cable promising a full report on the summit soon. The president took issue with those who argued that the participants had created a double standard for dealing with the Soviet Union and China. On Tuesday, the participants opened the door for loans to China, but Bush insisted that the fact that the group had maintained sanctions on China indicated that the leaders were still dealing firmly with the Chinese governnment because of the Tiananmen massacre last year.

On agriculture, the leaders urged quick settlement of issues that had deadlocked the United States and Europe over farm subsidies and had threatened to scuttle the current "Uruguay Round" of trade negotiations. Bush said the leaders had "also committed to maintain our personal involvement and to exercise political leadership at every step along the way."

"This is clear progress for both sides," Jacques Delors, president of the European Community, said. "Between friends, and inside the family, there are no victories. There are good compromises."

The dispute centered on the unwillingness of European nations to sharply cut subsidies to their farmers. Bush, who said a successful trade agreement would also mean reducing subsidies in the United States, surprised the Europeans with his intensity on the issue.

U.S. officials expressed pleasure today with the outcome, which was not hammered out until 4 a.m. this morning by aides. "We would like to get rid of these trade support subsidies . . . ," said Canadian Prime Minister Brian Mulroney. "The European Community argues that 'they're part of our culture.' Well, they're part of our culture too. But they cost an arm and a leg.

European leaders interpreted the final communique differently, indicating that hard bargaining still lies ahead before the trade talks, scheduled for completion in December, are judged successful.

"We don't want an imbalance in which European farmers would suffer," French President Francois Mitterrand said at a news conference.

The 16th annual economic summit was conducted against the backdrop of a year of upheaval in Europe and elsewhere, and the discussions here centered far less on traditional economic issues, such as exchange rates or coordinated policies to achieve economic growth, than on how the participating nations could adapt themselves to a world no longer dominated by East-West tensions.

In addition to Bush, Kohl and Mitterand, Mulroney and Delors, the participants were British Prime Minister Margaret Thatcher, Japanese Prime Minister Toshiki Kaifu and Italian President Giulio Andreotti.

The eight leaders arrived here divided over Soviet aid, with Kohl and Mitterrand pushing hard to help Gorbachev and Bush resisting. The study of the Soviet economy offered the simplest way out of their differences. A similar study was launched by the EC two weeks ago in Dublin; the agreement here brings the United States, Canada and Japan into the analysis of Soviet needs.

Treasury Secretary Nicholas F. Brady said the IMF likely would report directly to Bush, who would report to the other leaders. Brady added that the G-7 finance ministers might get an informal, interim report at their regular meeting with the IMF and World Bank this fall.

On the environment, the final communique set 1992 to complete negotiations on a framework for limiting or stabilizing emissions of gases that contribute to global warming. They also agreed to work with the new government of Brazil to preserve tropical rain forests, and agreed to begin negotiations on a "global forest convention" that they hope also to complete by 1992. The final environmental accord fell short of Kohl's desire for "radical" steps to limit "greenhouse gas" emissions, particularly carbon dioxide.

The Bush administration was on the defensive for opposing specific targets for reducing carbon dioxide and other greenhouse gases. Although environmental groups here criticized the final agreement, Bush said, "We came out with a reasoned position, not a radical position . . . ."

He sharply attacked the environmental groups, saying those on the "extreme . . . don't want to look down the road at the human consequence of men and women thrown out of work and families put into a whole new state of anxiety."

The summit communique skirted the issue of whether more scientific data is needed before moving to combat global warming, as the Bush administration contends.

Bush got a lukewarm response to his recently announced initiative to forgive or cancel Latin American debt and to his desire to see a comparable reduction in Polish debt.