With more than 200,000 members, the United States Chamber of Commerce has to lay out more than $40,000 in postage fees alone every time it wants to send them a message. And that's for a one-way communication, without response or follow-up.

So yesterday, the chamber, the world's largest business-lobbying organization, set up a cheaper, faster, and more flexible system of talking to its members and letting them talk back: its own television network.

From a fully equipped studio in its headquarters at 1615 H St. NW, the chamber will offer its members five hours a day of business-related programming on a nationwide network scheduled to begin transmitting on April 26, with full-time operation set to start in October.

The private television network will feature programs on business activities, lobbying, government regulation, taxes, trade and the economy for chamber members who will pay $5,000 a year to subscribe.

In a ceremony yesterday, the chamber's president, Richard Lesher, signed up the first subscribers: Atlantic Richfield Oil Co., PepsiCo Inc., LTV Corp., Armco Inc., Anheuser-Busch, and several local chambers of commerce.

Lesher said the organization's officials eventually "expect to see thousands of subscribers," involved in the chamber's live programs and participating by a two-way audio linkup in meetings "right here in this building."

The network, known as Biznet, was set up by Daryl Griffin, a former ABC television producer. According to Griffin, broadcast time on the relay satellite that Biznet will use costs only $600 an hour, which makes television communication much less costly than mail, as well as faster and more direct.

Griffin said the network will carry programs such as press conferences or briefings that are not reported by the commercial networks, analyses of economic and regulatory issues, live coverage of events important to the business community and reports on labor, small business and trade.

Much of it will make undramatic television, he acknowledged, but "we are not attempting to get high ratings or beat the networks . . . most of our programming is aimed at chief executives, and their tolerance level is higher."

Biznet is scheduled to begin transmitting April 26, showing an address by President Reagan to the chamber's annual meeting. It will broadcast once a week until October, then every working day from 9 a.m. to 2 p.m., with some programming repeated for West Coast subscribers. An hour each day will be set aside for an "interactive session," in which subscribers can talk directly to whoever is appearing at the time, Griffin said.

"We don't expect chief executive officers to sit around and watch TV five hours a day," he said, "but we will have program logs showing what is coming up, and they can designate someone to watch or tape it for viewing later."

Chamber officials said it cost about $4 million to set up Biznet. Griffin said it does not expect to break even on the service for at least a year. No commercials will be accepted, but the entire network will be available for rent when not being used for Biznet programs, Griffin said.

Programs will be transmitted "scrambled," or encoded, so that only subscribers who have a decoder can receive the broadcasts. In addition to the annual fee, subscribers will have to purchase dish antennas or cable connectors to receive the signals, but Griffin said they could charge those outlays off as capital expenditures on their corporate taxes