Japanese special envoy Nobuhiko Ushiba revealed yesterday at the end of four days' intensive trade talks with U.S. officials that his government is abandoning a traditional limit on deficit financing as one way of expanding domestic consumption in Japan.

American officials, who had been urging such a step, immediately labeled it "very encouraging," and said it would help assure realization of a newly announced 7 percent Japanese economic growth target for 1978. Faster Japanese growth is expected to attract more imports, and reduce tensions between that island nation and the United States.

Traditionally, Japan - with an eye on potential inflation - limits deficit financing to 30 percent of its national budget. Ushiba said yesterday that this figure could now go as high as 37 percent.

Nonetheless, U.S. special trade representative Robert S. Strauss reiterated that the total product of this week's negotiations on U.S.-Japanese trade problems fell short of hopes and expectations. "We have a long way to go." Strauss told a joint press conference.

This current round, in fact, adjourned with no agreement on the central issue - an American demand that Japan increase its imports sufficiently to guarantee that its massive trade-and-services surplus with the rest of the world will be eliminated.

Strauss said that he would go to Tokyo next month "to conclude what we began here" only if there is reason to believe - after Ushiba has reported American discontent to his government - that the "gap" between U.S. and Japanese views can be closed.

Officicals were more hopeful after yesterday's announcements by Ushiba than they were at the start of the week, when the Japanese package was limited largely to modest adjustments in tariffs and nontariff imports barriers.

A 7 percent Japanese growth rate, if achieved, would be significantly better than this year's 5.3 percent gain. But more importantly, the growth would come from the domestic, rather than the export side.

This would happen because the 21 percent rise in the value of the yen so far this year would tend to make Japanese exports less attractive, and because the Japanese plan to focus attention on domestic public works and more housing.

In turn, that would cut the Japanese trade surplus, now measured at $16 billion globally. And it would also trim the "current account" surplus, considered an even more important measure of a nation's financial relationships with the rest of the world.

The "current account" covers payments for such service items as insurance and shipping, as well as merchandise trade. Japan's current account is estimated to be in surplus by $8 billion to $10 billion his year - and that is the crux of the difficulties between Japan and here major trading partners.

Throughout this week's talks, American negotiators have insisted that Japan make a public commitment to let its surplus be turned around into a deficit, mostly by importing substantially greater quantities of manufactured goods.

"There is a real, conceptual difference between us and the Japanese on this issue," a high State Department official said yesterday. The American argument is that Japan, by running a current account surplus of $10 billion, adds to the already burdensome $40 billion oil cartel surplus. The total has to be financed by borrowing, which puts a strain on the monetary system.

"Japan profited in the postwar years by enormous exports to the rest of the world," the official said. "Now it has an international responsibility to share the world-wide oil cartel deficit, not to add to it."

But Japan sees it from another perspective. It argues that it needs enormous exports to finance its crucial imports of food, energy, and raw materials.

In an interview yesterday with The Washington Post, Ushiba acknowledged a "difference of opinion" on the key current account issue. He predicted that Japan might eventually work its way out of surplus, "but we have told them [only] that we shall not take any measures to prevent a deficit. But we can't make that a priority objective."

The American side, which in fact has set elimination of the current account deficit as the main priority, confirms that Ushiba took this position privately. "That's the reason," said one. "That this is going to be a long, agonizing series of negotiations."

Ushiba, who concluded his series of talks here with a courtesy call on President Carter, told reporters he understood that the U.S.-Japan talks were important for the rest of the world as well as the two principals. He is heading for discussions in Brussels with Common Market representatives before returning to Japan.

In response to questions at the press conference, he pledged that Japan would do its best to remove bureaucratic impediments to imports. But he insisted the Japanese market is more "open" than many critics contend.

He also predicted that the Japanese yen would not appreciate further, or might stabilize around current levels, as the Japanese current account surplus shows a declining trend. American officials said privately that Japanese fears of a further climb in the rate of the yen was a principal motivating force behind Japanese concessions.