President Reagan and the six other western leaders participating in the ninth economic summit here put aside their differences on world economic issues to join today in promising monetary and budgetary policies that they hope would promote recovery and reduce unemployment while also holding down inflation.

Flanked by all the others except British Prime Minister Margaret Thatcher, who left for home Sunday to resume her campaign for reelection, Reagan read a 10-point "Williamsburg Declaration" that pledged to "promote a sound and sustainable recovery" that would create new jobs not only in the rich nations represented here but also in the rest of the world.

The compromise communique and an annex contained a little something for each of the leaders of the United States, Canada, Britain, France, West Germany, Italy and Japan.

In a major concession to French President Francois Mitterrand, it directed their finance ministers to study ways to improve the international monetary system and to consider "the part which might, in due course, be played in this process by a high-level international monetary conference."

Mitterrand had proposed calling a meeting like the 1944 Bretton Woods Conference, which established the post-World War II monetary system. In being promised a study of the possibility of such a conference, Mitterrand achieved all that was politically feasible now, officials here said. U.S. officials would have preferred that the communique not specifically mention such a conference.

Mitterrand told reporters that the promise of a study "advanced the recognition of the need for international monetary reform. The idea has begun to penetrate . . . . The economic text goes further than the pessimists thought it would, and less than I had hoped."

In the annex to the summit declaration, the United States, Britain, France, West Germany and Japan also agreed to reinforce the International Monetary Fund's surveillance of their economic policies and performance to make it difficult to surprise each other with policy changes. In effect, they are supposed to coordinate their economic policies under the watchful eye of IMF managing director Jacques DeLarosiere.

They also agreed to consider fully the international implications of each nation's decisions on monetary, fiscal, exchange and employment policies. U.S. officials believe closer coordination of the major western economies would result in more stability in the exchange rates of their currencies and reduce demands for intervention to control painful fluctuations.

The Canadian government had hoped to join the other five in the IMF surveillance arrangement, which was initiated at last year's economic summit in Versailles. But it was not invited by the others here and will have to rely on informal contacts with DeLarosiere of the IMF.

After reading the summit declaration, President Reagan emphasized that there had been "no quick fixes" and said the leaders had met the tough issues "head on."

Suggesting that the declaration would bring a "message of hope to the peoples of the world and to future generations," he praised the other leaders for coming to Williamsburg with "a positive and common approach" that had produced a statement of "confidence, optimism, and certainty."

As Reagan announced that the tenth such summit would be held next year in Britain, Thatcher's chancellor of the Exchequer, Sir Geoffrey Howe, said in a statement that "the really striking feature of our discussions here has been the extent to which we share a common view and a common approach to the problems of managing our economies, and the emergence from recession."

The general thrust of the Williamsburg Declaration is that, while there are encouraging signs of economic recovery emphasized by Reagan and his officials, the basic challenge still facing the western world, as emphasized by the western European and Japanese delegations, is to ensure that the recovery endures.

The statement responded to frequently expressed concerns by the other leaders about big U.S. budget deficits by saying that all seven were committed to reduce "structural budget deficits, in particular, by limiting the growth of expenditures."

This carefully crafted language avoided any mention of raising taxes, to which Reagan is strongly opposed, and Treasury Secretary Donald T. Regan insisted at a news conference that no one in the summit sessions brought up the subject of raising U.S. taxes.

A commitment to try to keep inflation down has been a staple of all recent economic summit communiques. But the emphasis in the Williamsburg Declaration on the unemployment problem is new and reflects the deep concern of the leaders of western European nations about the enormous growth of joblessness in recent years.

The Williamsburg Declaration also fit the pattern of consensus at the meeting earlier this month in Paris of the foreign and finance ministers of the Organization for Economic Cooperation and Development. That group of 24 industrialized western nations emphasized a need to focus on economic growth rather than inflation control as the western world emerges from a severe recession.

With the example of last year's fractious Versailles summit fresh in their minds, the seven leaders and their ministers concentrated on achieving at least a surface compatibility of views. They appeared to have been successful, at the cost of eliminating most references to the many problems plaguing the western alliance recently.

The question of trade with the Soviet bloc, which was so divisive during and after the Versailles summit, was disposed of in a single paragraph saying East-West economic relations "should be compatible with our security interests."

Mitterrand observed this is "a reasonable proposition." Secretary of State George P. Shultz said agreement on this mention of East-West affairs had been reached after "a lot of activity and lots of disagreement, and everybody is, basically, on board."

Perhaps the potentially divisive issues, U.S. budget deficits and high interest rates, also were brushed over very lightly in the declaration, although West German economics minister Otto Lambsdorff said in an interview that "interest rates and the American budget deficit played a central role in this summit, and that was not to the delight of the American delegation."

The summit participants were aware that another failure on the scale of Versailles might have ended the summit process. "We can now all go back home and tell our people that there were no disagreements here," Lambsdorff said.

The language that may lead to a new global monetary conference was proposed by the French. It was adopted in place of alternate, weaker words suggested by the United States, which called for a study of the problems of the international monetary system but did not mention a new global conference.

In exchange for deferring to what Mitterrand wanted on the issue, the French agreed to the desire of the United States and West Germany to include a strong anti-protectionist statement calling for dismantling trade barriers. This part of the communique also called for a new negotiating round on world trade under the aegis of the General Agreement on Tariffs and Trade (GATT).

The French did succeed in having agriculture removed from this section of the communique. But the others succeeded, over French opposition, in including trade in services and in high technology products among the issues to be pursued by both the GATT and OECD.

An initiative successfully carried through by Canadian Prime Minister Pierre Trudeau of Canada resulted in the inclusion of a paragraph warning that the recent fall in oil prices should not weaken efforts to conserve energy and find alternative sources. Over an American objection, language was included saying that the leaders "all share the view that more predictability and less volatility in oil prices would be helpful to world economic prospects."

On the often controversial issue of currency exchange rate volatility, the declaration restated the Versailles summit agreement to promote greater "convergence" of economic performance as well as greater stability of exchange rates. The leaders also agreed they would "pursue closer consultations on policies affecting exchange markets and on market conditions," but U.S. officials insisted this would mean no basic change in present American intervention policy.

Regan acknowledged, however, that the leaders' intention was that their finance ministers should "meet more often, and make sure there is convergence. If someone is out of step, we should say so."

The declaration discussed the burdens that have fallen on developing countries during the recent recession and the seven leaders promised "special attention to the need of keeping a flow of aid and assistance going to poor nations, both through bilateral programs and through the international institutions."

They also promised to continue a dialogue with Third World nations and promised to cooperate in the forthcoming meeting of the United Nations Conference on Trade and Development in Belgrade early next month.

On the other hand, U.S. officials successfully resisted pressures for language that would have opened the door to enlarged funding for the soft-loan affiliate of the World Bank. The language of the declaration merely reaffirms commitments to provide "agreed funding levels for the International Development Association."