Secretary of State Alexander M. Haig Jr. and Foreign Minister Andrei Gromyko completed the highest level round of U.S.-Soviet talks of the Reagan administration tonight with agreement on continuing their dialogue but apparently on very little else.

The five-hour session, like a four-hour meeting last Wednesday, was primarily a head-to-head meeting of the two ministers without advisers.

When it was over, State Department Spokesman Dean Fischer said the meeting had been "frank, businesslike and serious," but he discouraged any suggestion that substantive progress had been made between the two nuclear superpowers.

Fischer did announce that Haig and Gromyko planned to continue their talks early next year, perhaps in Geneva.

Gromyko is not being invited to the White House as he was during his annual United Nations pilgrimage in previous administrations. The thinking in omitting such an invitation, according to sources here, is partly to let Gromyko know that "business as usual" does not prevail in the Reagan administration.

The tentative selection of the Geneva site also means that Haig is not being invited to Moscow. Thus the top-level perceptions that the two leaderships have of one another is limited, at the moment, to the unusually lengthy and unusually secretive discussions between their foreign ministers here in these opening weeks of the U.N. General Assembly.

Of the five-hour session today at the Soviet Mission to the United Nations, all but the final half-hour was a private Haig-Gromyko meeting with only interpreters also present. Nearly three of the four hours of last Wednesday's meeting also consisted of a one-on-one encounter.

Fischer had no explanation for the unusually restricted nature of the meetings, except to say that the two men preferred it that way. Such meetings are thought to reduce the need and incentive for posturing for the diplomatic record.

A major part of today's meeting concerned bilateral issues between the two nations such as trade and economic relations, which were not covered last Wednesday. Fischer also said that "humanitarian questions," apparently referring to such matters as the emigration of Soviet Jews, were discussed today.

Another topic in the final meeting was the negotiations scheduled to begin in Geneva Nov. 30 between the two nations on the limitation of medium-range nuclear forces in Europe. The announcement of these negotiations following last Wednesday's meeting was, as expected, the only substantive accomplishment of the Haig-Gromyko talks.

Even this accomplishment was a highly qualified one, in view of the continuing disagreement between the two sides about the weapons to be included in the negotiations. Last week's announcement resorted to unusual vagueness in describing the subject of the talks, saying only that they would cover "those nuclear arms which were earlier discussed" during informal exchanges between U.S. and Soviet diplomats late last year. At that time, the diplomats disagreed on what weapons systems were to be limited, with the Soviets pressing for a more extensive list than the United States.

U.S. sources told reporters that the vague wording resulted from more than an hour of Soviet-American haggling toward the end of last Wednesday's meeting.

"Everything on our agenda was touched upon" in the Haig-Gromyko talks, Fischer said. He would not specify this agenda, but Haig said before the meetings that he anticipated exchanges on Afghanistan, Cambodia, the activity of Soviet allies such as Cuba in the developing world and future Soviet-American trade and economic relationships, among other things.

"The outcome of the meetings essentially met our expectations," Fischer told reporters. These expectations, as expressed by U.S. sources in advance, were that the two sides would disagree sharply on everything except the opening of the European missile talks, but that precise understanding of each other's positions could be obtained and the stage set for a continuing dialogue.