Cable is making inroads on broadcast TV, but...

Commercial over-the-air television is playing its own version of the numbers game. But just about all it seems to be able to do is watch nervously as cable creeps up on it.

According to the A. C. Nielsen Company, 34 percent of all US households as of July 1982 (the latest monthly report) were wired for cable. This means an estimated 27,884,000 US households now have cable TV service compared with the Nielsen estimates that there are, in all, about 81.9 million American TV households with over-the-air TV.

Some experts predict that cable will reach 90 percent penetration by 1990.

It is perhaps significant to note the vocabulary for cable. Nielsen refers to ''homes penetrated'' when it means homes that are actually wired for cable. But cable companies tend to talk about ''homes passed.'' This allows them to cite larger numbers about their service, because ''homes passed'' includes homes close enough to cable lines that residents could subscribe to the cable service if they wished.

However, as more and more cable companies find the financial going rough, it begins to look as f many experts have misinterpreted the electronic future by overestimating the long-range

impact of cable. DBS (direct broadcast satellite) may very well turn out to be the major communications medium during the coming electronic age.

A new report from a market research company, International Resource Development, projects that by 1990 more than 15 million American homes should be equipped with rooftop ''dishes'' (earth stations) that would allow them to receive satellite transmissions directly. The report estimates that within a few years mass-produced dishes will be generally available for under $500.

By the end of the decade cable may be used mainly for two-way transactional services such as shopping, banking, alarm systems, and so forth.