Britain's rush into the world of advanced cable TV systems reaches a crucial stage this month. The end of August is the deadline for applications to the government to build a series of pilot projects that should demonstrate Britain's readiness to move ahead in cable technology.
Kenneth Baker, the minister for information technology, who is the driving force behind the government's cable plans, is determined that the projects feature the most advanced technologies possible.
The Department of Trade and Industry, which will decide on the individual projects, will give precedence to those that offer two-way communication. This is instead of the one-way message traffic which is all that's possible in ordinary cable TV systems, for example.
Mr. Baker says two-way capability will mean the systems will make possible a range of new services, doing something to offset the downturn in Britain's traditional manufacturing industries such as steel and autos.
Such services could include home banking, ''teleshopping,'' or house surveillance systems. In all uses, computer messages are required to pass in both directions between equipment on domestic premises and a central control station.
Almost certainly, however, the first cable systems will at least initially emphasize good old-fashioned cable TV, if only because this is what consumers recognize and are prepared to pay for.
Baker and other government officials have theorized for the past couple of years about what cable can offer Britain. But the applications for the pilot projects will test whether private companies are ready to take up the challenge.
Britain's Conservative administration has shunned the idea that British Telecom, the state-owned telecommunications authority, should do most of the work in laying the new cable.
Instead, private companies will be entrusted with the job. (As part of the government's ''free enterprise'' policy, it is selling shares in British Telecom to make it private in a couple of years.)
Under the government's plan, it will give franchises to up to 12 cable projects in the pilot program. Officials will have selected them by November, leaving the systems ready to start up next year.
The idea is that up to 100,000 homes will be cabled in each of the pilot projects, each costing $:15 million to $:20 million ($23 million to $30 million) , depending on the degree of complexity.
Most probably, each project will be administered by a consortium of private companies. In recent months there has been a tremor of activity as electronics companies such as Thorn-EMI and Rediffusion form consortia with others, such as advertising or entertainment firms.
Oak Industries Inc., General Instrument Corporation, and Scientific-Atlanta Inc. are among American companies that have indicated they may work with consortia.
In the government's plans, the first set of cable projects will be just the start of a series of systems that will gradually cable up most of the populated areas of Britain. Each cable system will be linked to the ordinary telecommunications network so as to carry voice traffic.
Eventually, a new government body called the cable authority will regulate the spread of the new systems. The authority has still to be established, since Parliament has not yet passed the legislation.
Opinions vary as to how well cable will catch on. Charles Read, director of information technology at the post office (the government body that handles the mail system), says that within 10 years half of Britain's 20 million homes will be cabled. He says the growth in cable will be much faster than in the United States. As a result of the advanced services that the systems will feature, consumer demand for cable links will increase rapidly, Mr. Read says.
Other observers are not so sure. Prof. John Ashworth, a former chief scientific adviser to the government, who is now the vice-chancellor of Salford University, regrets that the government is not taking a stronger lead in planning the cable systems.
He says the government should be more closely involved, for example, in setting technical standards.
As an example of poor planning, Professor Ashworth cites the growth of Britain's rail network early in the 19th century. Lack of foresight then led to decades of confusion as railways laid by rival, privately owned companies straddled the country but would not link up. Ashworth says the muddle that existed then should not be repeated with cable.