Syria is braced for the upcoming visit of Libyan leader Muammar Qaddafi with a mixture of hope and apprehension over the two nation's recent agreement for a total merger into one state.

The scheme is being taken seriously here because it offers Syrian President Hafez Assad not only a way out of his increasing regional isolation but more importantly, perhaps access to Libyan oil wealth to pay for new Soviet arms and offset the expected loss of several hundred million dollars in Iraqi financial assistance.

The merger plan and Qaddafi's visit have taken on added importance in the wake of Iraq's severing of its diplomatic ties with this country two weeks ago and Syria's signing of a treaty of friendship and cooperation with the Soviet Union, which could be a prelude to a similar one with Libya.

There are reports circulating here and in the Beirut press that Qaddafi will fly to Moscow before the end of this month -- and there is speculation that he, too, will sign a treaty.

Since Syria and Libya have agreed to merge into a single state, it would seem logical for Libya to accept a more formal relationship now with Moscow in order to align its foreign policy with that of its Syrian partner. But logic is not always a good guide to Arab behavior. And there are doubts here about the Syrian-Libyan unity accord.

Syrian officials are exhibiting the caution of a thrice-divorced wife -- which Syria in effect is where merger attempts are concerned -- about how fast and how far the two nations can move in this latest Arab effort at marrying two rather disimilar countries separated by 700 miles of Mediterranean Sea.

As a result, Western observers here expect the facade of a unitary state may be established, behind which Syria will resist the anticipated pressure from Qaddafi for a far tighter merger.

Whether this will satisfy the visionary Qaddafi sufficiently to open Libyan coffers to pay for the Soviet arms Assad covets and buoy the Syrian economy will become clear with time.

Perhaps hoping to provoke a selffulfilling prophesy, a top Syrian official has leaked a story to the press that Libya already has sent $1 billion to Moscow to cover Syrian arms purchases and $600 million to Syria in financial aid.

Western Sources and Syria's economics minister confirm the arrival here of only $100 million of this amount since the Sept. 10 announcement of the unification agreement.

There already has been a delay in implementing the plan, since the two leaders initially agreed to meet "not later than one month" after the signing of the accord to discuss details.

Meanwhile, Syrian officials do not hide their intention to proceed with due caution. And they have moved quickly to reassure the jittery Syrian business community -- whose opposition sowed the seeds for the collapse of an earlier unity attempt with Egypt -- that their interests will not be adversely affected.

"We shall try to undertake unitary steps very cautously and see that a sound basis is established," said Mohamed Atrash, Syria's economic minister, in an interview with The Washington Post. "Definitely, it will not be established overnight."

Information Minister Ahmad Iskandar perhaps revealed the nature of Syria's delaying tactics when he said in a separate interview that "the masses have to be involved indeciding the formula for the new state.

"We understand the [unity] process as one of interaction between two regions and not the extension of one region to include the other," he continued. "For the time being, everything will stay as it is now. No one can predict the future whether they will accept the Baath Party experience or we will accept the Libyan experience."

At the same time, Iskandar noted the similarities underlying the two regimes that are working to make a merger feasible. Both, he said, were Arab nationalist, progressive and socialist and both had a "heritage of struggle" in their respective revolutions.

As fr the very different internal political structures of the two nations, Iskandar tried to play down this potential obstacle by suggesting that the nature and work of the Syrian Baath Party and the Libyan Revolutionary People's Committees were basically similar.

There is no party at all in Libya, and Qaddafi has tried to put power directly into the hands of the people through a system of people's committees, set up inside ministries, factories, farms, embassies and even the Army, that has raised havoc with the normal functioning of his government.

Syria, by contrast, is run strictly from the top down under the Baath Party, a tightly knit, hierarchical structure modeled after the East European communist party systems, though the ideology is different.

The Syrian attitude toward the idea of Arab unity if full of ambiguity. On the one hand, it is the first declared objective of the Baath Party, whose motto is "unity, freedom and socialism," and Syria's claim to Arab world leadership is based partly on its commitment to fulfilling the centuries-old dream of pan-Arabism.

Behind all the rhetoric, however, Syrians have learned the hard way to approach unity schemes with a degree of realism, having lived through at least three failed attempts.

The first and longest was with Egypt in 1958 under the United Arab Republic, which broke up three years later in considerable Syrian bitterness over heavy-handed Egpytian attempts to impose its economic system on this country.

Then, in 1972 Syria agreed to a merger with Libya, Egypt and the Sudan in the Federation of Arab Republics, which quickly fell victim to the October 1973 Arab-Israeli war.

Again last year, Syria and Iraq signed a unity pact but it never got off the ground, and Iraq now has broken relations with Syria over alleged Syrian military assistance to Iran.

Many Western observers here feel that Syria has a strong economic rationale just now for allowing itself to be stampeded into yet another unity attempt.

Last year, Syria received $1.6 billion in Arab financial assistance under the so-called Baghdad Agreement of 1978 to help states directly confronting Israel. This accounted for almost one third of Syria's combined regular and development budgets.

Even with this massive aid, Syria experienced an acute shortage of hard currency at midyear, forcing it to delay some development projects and leaving it unable to cover letters of credit.

Of the amount that Syria received in Arab aid last year, $270 million came from Iraq, according to State Department testimony before Congress earlier this year.

Iraq already has failed to make the final installment this fall on its promised aid to Syria, Atrash confirmed, and it seems likely that in the wake of Iraq's break in relations with this country the Iraqis will stop making payments altogether.

Whether Libya will come through to offset this loss remains to be seen. Western observers note that Libya was the only Arab country not to live up its obligations to Syria under the Baghdad Agreement of last year. Libya gave just $50 million of the $1.6 billion that Syria received.

Sources here say that the Libyan money went primarily to replace 10 Syrian Mig jets shot down in combat with Israeli warplanes during 1979.