Suleyman Demirel, Turkey's pro-West prime minister, has lost his majority in the ruling National Assembly but the prospects of his administration's survival appear to have grown rather than diminished.

The reason for this paradox is that the opposition parties, which now control a majority, are more opposed to one another than to the government.

Thanks to his unusual phenomenon, Turkey yesterday avoided a government crisis when the opposition parties moved to oust Demirel but ended up by mangling one another.

The no-confidence motion was made by former prime minister Bulent Ecevit, a social democrat and main opposition leader who was counting on the support of Necmettin Erbakan and his small Islamic fundamentalist National Salvation Party. Erbakan had withdrawn his party's support from Demirel, leaving him with the backing only of the ultrarightist Nationalist Action Party led by former Col. Alpaslan Turkes.

Erbakan hinted that he would help Ecevit topple the government on condition that they agreed on a new government. But because Erbakan's political ambition far surpasses his power in parliament there was no agreement. With 22 seats in the 450-member assembly compared with Ecevit's 205, Erbakan demanded the prime minister's post himself.

When Ecevit refused, Erbakan deserted the social democrat at the last minute yesterday. That caused Demirel to win a vote of confidence and reaffirmed the parliamentary saying that "if you are going to climb down a wall, don't use Erbakan's rope."

The possibility of a government crisis appears to have receded with the oppositions rout yesterday. Ecevit is facing an incipient revolt in his party and he will probably be forced to concentrate his energies on keeping his seat rather than unseating others. Erbakan appears to have lost the last vestiges of his credibility.

Demirel will now be almost certain to rule until the next general election in June 1981. The conservative prime minister consequently will be in a position to apply his policies of encouraging free enterprise, which are being backed by substantial Western credits and are beginning to show positive results in bolstering the country's ravaged economy.

He will also have freedom to pursue his pro-West policies in foreign affairs improving relations with the United States, mending fences with Greece and applying for full membership in the European Community.

Demirel's strict economic stabilization measures have caused much misery but are beginning to yield good results. Inflation has dropped from a monthly average of more than 7 percent to less than 3 percent. Western aid has eased the shortages which had been plaguing industrialists and housewives alike. There is hope that if Demirel stays in power and perseveres, the crisis can be overcome.

Jubilant after his parliamentary victory, the hefty Demirel, who has been a dominant figure in Turkish political life for more than 15 years, appeared undaunted by the problems. "We are on the right track," he declared. a"We are traveling toward daylight. It is for this reason that those who have been declaring Turkey the 'sick man of Europe' are now rushing to its aid."