North Sea oil industry is on the verge of a new surge

The North Sea petroleum industry is off and running again - toward a recovery that could set off a new round of exploration and development. The recovery, coming after a year of decreased demand which has brought severe liquidity problems to oil operators here, could make North Sea oil one of the few bright spots in an otherwise depressed worldwide petroleum industry.

For Scotland, this could not come at a better time. ''It's still a depressed economy here,'' says David Crichton, an economist at the Scottish Development Agency, a national industrial development organization based in Glasgow. ''We've got 16 or 17 percent unemployment. If it weren't for the North Sea, it would be much worse.''

The agency forecasts that in the course of the 1980s, 50 new fields will be coming on in the United Kingdom sector of the North Sea and 75 new fields in the 1990s. The new fields will require hardware costing an estimated $120 billion. At present, there are 20 producing fields there.

In a move to spur development, the British government has announced a series of offshore tax relief measures, worth about $1.2 billion, to major producers over the next four years. The cuts are to stimulate exploration and development - mainly in the smaller, marginal fields of the future - and to extend Britain's self-sufficiency into the 1990s.

As a result, Shell Oil Company, which produces 750,000 barrels a day of North Sea crude, has announced plans to spend between $500 million and $600 million annually for an oil development program in the North Sea. That makes it the first major oil company to take advantage of the tax cuts. John Raisman, Shell's U.K. chairman and chief executive, called the cuts a ''positive stimulus'' to development.

Because of the improved tax situation, Shell U.K. has revived two previously shelved projects - the northerly Tern and Eider fields. Shell said appraisal drilling would be carried out later this year so that development decisions could be made early next year.

Other companies are weighing the tax benefits. ''Don't expect too many surprises,'' cautioned an official of Britoil, the exploration and development arm of state-owned British National Petroleum Corporation (BNOC), which leads the way in North Sea oil pricing.

He said, however, that the incentives have improved ''the economics'' of the Clyde field, which Britoil is developing. The Clyde is not expected to produce oil until 1987. Britoil, traditionally an active explorer, has been less aggressive recently in the North Sea. The company operates two producing fields, Thistle and Beatrice.

Officials of the Standard Oil Company of Indiana, another large North Sea producer, noted that the government's action should hasten development, but declined comment on future plans.

The United Kingdom is now the fifth-largest oil producer and a net exporter of oil and gas. Total North Sea oil production is estimated at 2.9 million barrels a day. About 2.3 million barrels of that come from the British sector, with just over half of it going to BNOC through various royalty and participation agreements.

With the swift pace of changes recently, there is a mood of optimism in the industry here. Nowhere is this more evident than among the scores of United States-based companies that produce the parts for the well-and-rig assemblies that support the producing efforts of companies like Shell, Standard of Indiana, Texaco Inc., and other ''majors'' operating here. The total volume of orders placed by these companies has averaged about $6 billion annually, according to the British Department of Energy.

Since the early 1970s, an estimated 200 US-based companies have flocked to Scotland seeking joint ventures with Scottish- and British-based companies and additional market outlets.

The spinoff effects have resulted in enormous growth for Scotland's economy. Harbors have been expanded, dock entrances deepened, airport facilities extended , terminals constructed, new supply bases built, massive road improvements undertaken, and construction yards set up.

One company riding the crest of this boom is T. K. Valve Ltd., of Dunfermline , a town in the Fife region. ''We've not really been subject to the slump - probably because we're so heavy into exports,'' said Martin Wallbank, supervisor of sales administration.

The Scottish subsidiary of Sooner Pipe & Supply Inc., based in Tulsa, Okla., produces pipeline ball valves. A recent $13 million expansion is expected to raise employment to 500 from its current 300. Annual sales are $25 million, and Mr. Wallbank looks for sales to triple by year's end.

He says orders are so plentiful that the Scottish subsidiary now accounts for 70 percent of total companywide sales. In 1974, when T.K. Valve began operations in Scotland, it sold most of its products to North Sea customers. Now, it exports about 75 percent of its output to foreign markets.

While government and industry officials here are optimistic that conditions in the North Sea oil industry will improve, they concede that much will depend on whether oil prices stabilize and if the pace of commercial development of the smaller, more marginal fields - which now account for the bulk of North Sea discoveries - is fast enough to maintain current production levels.

''If we have a high level of exploration, we're pretty confident we're going to get a high rate of development,'' says the Scottish Development Agency's Mr. Crichton.