By Yuki Noguchi Washington Post Staff Writer    CityNet Telecommunications Inc., a company that lays fiber-optic cables in sewer pipes, plans to announce in coming weeks agreements that will allow the company to construct networks in Dallas and Pittsburgh.    The Silver Spring-based firm typically signs agreements for the rights to send its robots into the sewers to lay cable, then it leases those cables to telecommunications carriers seeking high-capacity connections into major office buildings.    In turn, each of the cities contracted with CityNet receives payment from the company in the form of shared revenue. Each municipality will get 2.5 percent of CityNet's gross revenue in that city. The big advantage is that cities don't have to deal with buckled streets from repeated digging and trenching by companies that lay their cables under the roads, said Robert G. Berger, president, chief executive and founder of the firm.    Dallas, a customer CityNet plans to announce Thursday, will be its largest city to date, with about 250 downtown buildings to be hooked up in its initial phase, said Lee Allentuck, a spokesman for the company. Pittsburgh, which will be announced in the coming weeks, will be CityNet's ninth urban market.    CityNet officials will also turn to bringing in revenue, something the company hasn't done during its initial buildout in metropolitan areas. Berger said the company plans to sign on several carrier customers in the next couple of weeks. The deals will be 20-year leases paid upfront, but Berger declined to disclose the details.    By another measure, the ability to raise money, the company is doing better than most of its peers: In April, it signed a deal for an additional $275 million in private financing. That was on top of its initial round of $100 million in financing last year. Separately, the company also plans to announce today that it completed construction in Albuquerque, its first market. More stories in TELECOM online at Washtech.com