The most important Soviet-American talks of the Reagan administration have left the two sides at loggerheads on a long list of international issues with little promise of an early breakthrough, according to the account of a senior U.S. official who took part.

The American view of the nine hours of talks between Secretary of State Alexander M. Haig Jr. and Soviet Foreign Minister Andrei A. Gromyko suggests a long road ahead before the Kremlin agrees to "a whole new character" of superpower relations that the Reagan administration is insisting upon.

Even the single substantive achievement of the Haig-Gromyko talks, the agreement to begin negotiations Nov. 30 on medium-range nuclear forces in Europe, is only the beginning of "very difficult, perhaps prolonged" talks on this issue with "unreasonable initial Soviet positions," according to the U.S. account. One "particularly interesting" aspect of the European missile discussion, which caused a flurry of speculation in the U.S. camp, is a reported Soviet effort to disassociate this issue from forthcoming strategic arms negotiations.

About the only saving grace about the discussions with Gromyko, as described to reporters here, is that everything brought up by either side was discussed and that the dialogue will continue early next year. But American officials are not holding out any expectation for a major improvement in superpower relations at that time.

An unusually detailed account of Haig's two lengthy meetings here with Gromyko, most of which were head-to-head talks with only the two ministers and their interpreters present, was provided on condition that the authoritative U.S. source not be mentioned by name.

For his part, Gromyko was reported to be more optimistic, at least in his initial description to Western visitors. According to diplomatic sources, Gromyko told Canadian Secretary of State for External Affairs Mark MacGuigan that he found the discussions with Haig "encouraging."

The lion's share of the American presentation in the Haig-Gromyko talks, as described by the U.S. source, was devoted to extensive discussion of geopolitical and regional conflicts between the two countries. Haig is reported to have made the case for "the interrelationships of Soviet activity worldwide to the overall character of our relations." This is the "linkage" principle of Soviet-American relations that the Reagan administration has expounded and the Soviets have rejected.

First on the list of the questions raised by Haig, and given special emphasis in the account to reporters, was "the important issue of Cuba," particularly Soviet support of large-scale Cuban military forces at home and "their interventionist policies" in Africa and the Western Hemisphere.

There was no report of Gromyko's response to Haig. The Soviet minister, in his Sept. 22 speech to the U.N. General Assembly, went out of his way to demand that the United States cease stepping up "hostile, criminal intrigues against Cuba."

Other matters reportedly raised by Haig included Soviet activity involving Afghanistan, Cambodia, Pakistan, Iran, the Persian Gulf, Libya, the Middle East and Poland. "The shadow of Poland" falls over arms control talks and all other East-West issues in Haig's view.

Haig also is said to have raised the U.S. charges of a "yellow rain" of toxins in Cambodia, the Helsinki follow-up conference in Madrid, specific human rights and humanitarian cases in the Soviet Union and the overall topic of emigration from the Soviet Union.

Haig told Gromyko that "the United States cannot accept recent patterns of Soviet international behavior," reporters were told. Bringing about the desired change in Soviet behavior will be a long and perhaps tedious process, in the U.S. view, requiring "a continuing high level of Western unity" and especially a continuing and visible U.S. determination to increase its military strength.

Moscow was said to be pressing for agreement on broad principles rather than on specific problem areas, "with emphasis on equality in a broad sense, especially in the security field."

Other matters of particular concern to the Russians in the Haig-Gromyko talks, according to the U.S. account, were:

* Strategic arms limitation. Haig emphasized that the SALT II treaty "is behind us," requiring a new basis for SALT. This and other arms control issues are likely to be discussed in the projected Haig-Gromyko meeting early next year. Despite speculation to the contrary, the U.S. official said that meeting will not be the vehicle for reopening negotiations.

* Trade prospects with the United States, which were "closely related" by Haig to overall Soviet international behavior.

* U.S. rhetoric, which the Russians find offensive. Haig is reported to have told Gromyko that the Soviet Union cannot expect restraint in U.S. rhetoric while engaging in "outrageous, propagandistic patterns" of its own.

As described by the U.S. official, the two sides begin far apart on the European missile negotiations scheduled to start Nov. 30 in Geneva. Moscow wants limitations to apply only to weapons in the European part of the Soviet Union, but Americans want "global" restraints, especially on the SS20 mobile missiles. The Soviets want to include forward-based systems of all kinds, while the United States wishes to concentrate initially on medium-range, land-based missiles. Verification, the U.S. source said, will clearly create "contentious problems."

From the U.S. side there was only speculation, but lots of it, about the apparently unexpected Soviet effort to disassociate the European missile negotiations from the forthcoming SALT process. One theory is that the Kremlin has serious hopes of restraining U.S. deployment of new medium-range missiles and does not wish to have this prospect clouded by involvement with SALT.