The Soviet Union has brought up a major share of the available world supply of cobalt in recent months in apparent anticipation of a global shortage, dealers in the strategic metal said here yesterday.

The shortage is now an accomplished fact. The abortive invasion of Shaba Province in Zaire has shut off 65 percent of the world's cobalt supply for up to nine months. Cobalt is used in so-called super alloys required for jet engines, missiles and submarines.

All this year, dealers reported, the Soviets, Poles and East Germans have been "steady and substantial" buyers on London's free market. They got in well before the price rises of the past two months that have carried cobalt from $7 to $20 a pound, with more increases to come.

"They had a shrewd inkling of what was going to blow," said Luf Lubett, director of Ayrton and Partners and chairman of the Minor Metals Traders Association. "I was pre-emptive buying in expectations of a shortage."

French and U.S. officials have charged that the guerrilla force that invaded Shaba Province had been trained in neighboring Angola by Cuban military advisers with Soviet support.

The United States has about 41 million pounds of cobalt stockpiled, a little more than four years supply based on current consumption rates, according to the U.S Geological Survey, with 71 per cent of it imported from Zaire.

The rest comes from Finland, Norway, Morocco and a variety of other countries. The United States stopped producing cobalt, which is almost always a by-product of copper mining, in 1971.

The free market in cobalt and other metals is small, with perhaps 20 dealers taking part. So information spreads rapidly.

Lubett's conclusion, however, is necessarily an opinion.Neither he nor the one or two dealers through whom the Soviets habitually buy know precisely how much Moscow has purchased and, of equal importance, how this year's buying compares with last.

The Soviets have been building up their stocks of cobalt since late in 1976. At best, the dealers can only guess that the 1978 purchases were abnormal.

The dealers say the Soviets have been exceedingly canny buyers, placing orders of only 30- to -50 tons at a time. Deals in the free market cover perhaps 10 percent of the world's output - about 25,000 tons - so orders of this size would be noticed but not disruptive.

The Soviets, moreover, bargained strenously over every purchase. "I offered them some cobalt at $8 a pound but they held our for $7.60," one dealer recalled. If Moscow knew that the world's supply was going to be interrupted, it did not give the game away.

Until the invasion, most dealers here attributed the free market rise of nearly 200 percent to conventional economic forces - a month-long strike at the Belgian plant treating Zaire's concentrates and production problems in Zambia, the distant second producer.

Most of the metal is sold through the bulk market, directly from big producer to big customer. The price on that market has risen far less. On Monday, Zambia announced that it would riase its bulk price by about 30 percent, to $8.50 a pound. Further increases are expected, but nothing likde those on the free-wheeling free market.

Lubett, mining engineer, thinks Zairian mines will be down at least six and possibly nine months. He predicts free market increases of several hundred percent during this stretch. Tuesday, buyers seeking cobalt at $30 a pound, another 50 percent rise, found all the sellers refusing to deal.

Rough estimates of the Soviet purchases this year range from 500 to 2,000 tons. Assuming they bought in near $8 a pound and picked up 2,000 tons, they have made a $35 million investment in a stockpile now worth $13 million and heading higher.

The Soviet Union, however, is far less interested in speculative paper profits than in an assured supply of a vital metal.

If Lubett's most pessimistic forecast is correct, the world will lose almost half a year's cobalt output. Other metals can be substituted in alloys for cobalt but the changeover is expensive and time-consuming.