As the Saharan desert war heats up between Morocco and Algerian backed Polisario guerrillas, American policy shows signs of shifting toward, more pronounced neutrality. In effect, the Carter administration has signaled it wants to safeguard the growing American stake in Algeria.

While the United States has avoided any step toward recognizing Polisario - a movement seeking independence for the phosphate rich Sahara instead of the existing partition of the former Spanish territory between. Morocco and Mauritania - diplomats here point to recent "American failures to do things which would have been normal." They were referring to the total backing former Secretary of State Henry Kissinger gave to King Hassan's aspirations to integrate the Sahara into a greater Morocco.

In particular, the United States, for the first time, is understood to be considering a substantial contribution of relief funds to Saharan refugees under Polisario control. Washington ignored earlier U.N. appeals on the refugee's behalf.

In addition, American sources consistently decline to confirm Hassan's accusations of Soviet and Cuban penetration of Polisario.

American military assistance to Morocco continues, but it has shown no signs of changing character to help Hassan wage his desert war. France, not the United States, has stepped up military and political support for Morocco, notably in the form of sophisticated Mirage figther-bombers.

French help to Morocco has aroused ire among radical African and Arab governments, particularly Algeria. It also has angered Polisario, which shows no readiness to release six French hostages and now threatens to treat French and other foreigners working in Morocco and Mauretania as "mercenaries."

Meanwhile, the United States has supplanted France as Algeria's principal trading partner, and with $8 billion in American investment, the Algerians know they have a good deal of moral protection.

Besides protecting the Algerian connection, the neutral American stance appears designed to minimize the risks of Moroccan-Algerian war and the prospect of a superpower confrontation in northwest Africa.

Diplomats here point out that the State Department does not ostracize Polisario representatives in the manner it does, the Palestine Liberation Organization, for instance.

Any American relief contribution for refugees. which one source said might cover a fifth of the U.N. appeal for $5 million, would undermine the Moroccan contention that the Saharan refugees ranks are swollen by tribesmen from neighboring desert countries.

The U.S. funds presumably would help Saharans both in the "Saharan Arab republic" proclaimed by Polisario in what has been Moroccan territory and also in Algeria, where some refugee camps and guerilla sanctuaries are located.

American spokesmen also conspicously avoid publicly confirming Hassan's accusations that Polisario itself contains Algerian troops or other non Saharans, that Polisario has Cuban advisers or is a Communist-dominated "Trojan horse" for Soviet influence.

On the contrary, some American analysts point out that Cubans are not known to be helping Polisario militarily. Algeria , which provides Polisario's main military support, is thought unlikely to allow Cuban, Soviet or Libyan influence to grow too strong on Algeria's own border, these sources point out.

American military assistance continues to Morocco, but at the same time, the first American military mission in many years has just visited Algiers. It was certainly told of Polisario's current military successes, which contradicted intial forecasts of an easy Moroccan victory and have increased Polisario's credibility. Polisario raiding parties into the desert have returned with Moroccan prisoners and captured armaments.

POlisario guerrillas appear to have neutralized Moroccan airpower in the desert, although the terrain is favorable to airstrikes. An undisclosed number of Morocco's American-supplied F-5s have been shot down by Polisario guerrillas using Soviet-made, shoulder-fired SAM-7 missiles or 50-caliber machineguns.

The experience has made Moroccan pilots wary, and the Polisario more confident. "Now they fly high and missus, or they fly low and we shoot them down." guerrillas say. "Either way they don't bother us.