Cable TV industry efforts to place ads on the broadcast networks promoting new cable customer-service guarantees have run into a snag: CBS and NBC won’t carry them, and ABC says it’s balking until the accuracy of the promos can be verified.

Big Three web reluctance in airing the ads won’t stop the cable industry, which on March 1 is launching a $6 million TV ad blitz on Fox and 25 top cable networks. The blurbs promise free cable installation to new customers if an installer misses an appointment, and a $20 rebate for late service calls.

The ads, unveiled Feb. 21 at the National Cable Television Assn. headquarters here, feature the cable on-time guarantees along with shots of UPS and FedEx trucks.

By aligning itself with UPS and FedEx, the cable industry hopes to convince viewers of the seriousness of their commitment to customer service, said HBO senior veepee Denny Wilkinson, who worked on the ad campaign.

Both CBS and NBC declined to carry the ads because of company policy that bars promos of competitors, according to network representatives. An ABC spokeswoman said the Alphabet web is awaiting substantiation from the cable industry on claims made in the commercials before the ads will be carried.

Wilkinson said the Big Three networks have “chosen (not) to support a business that is clearly their competitor.”

NCTA president Decker Anstrom said cablers do not be-grudge the decision by broadcasters not to carry the ads. Anstrom added, however, that cable “looks forward to taking more and more of their (broadcasters’) market share.”

Anstrom said the customer service ads are designed to “close the credibility gap” between cable operators and viewers.

The cable industry intends to spend $4 million on the 30 spots in the first two weeks of March. Cable networks themselves plan to make available $2 million worth of free air time in succeeding weeks. Wilkinson said the blanket coverage is designed to ensure that 90% of U.S. TV households see one of the ads.