The U.S. Postal Service has allowed Western Union to end a 15-month-old agreement to provide telecommunications technology for the postal service's planned electronic message-delivery system. t

Postal customers with the necessary computer capability would be able to send messages electronically through a medium such as Western Union to 25 specially equipped post offices around the country under the planned system.

At those offices, customers' messages would be printed electronically, mechanically placed in envelopes and mailed. The system would cut mailing time -- including message preparation -- down to two days from anywhere across the country, postal officials said.

However, several bureaucratic delays involving the Federal Communications Commission and the Postal Rate Commission have held up implementation of the system, according to Postmaster General William Bolger.

"Recently I met with the president of Western Union to jointly assess our respective positions," Bolger said. "I was informed that Western Union could not visualize any immediate likelihood of regulatory approval that would allow for the startup of (the system) any time soon and that it was therefore requesting to withdraw from its contract with the Postal Service. I consented."

Despite Western Union's withdrawal, Bolger said the postal service plans to trudge ahead with it plans and is seeking other bidders to provide the electronic communications service from the customers to the post offices.

Meanwhile, the postal service Board of Governors yesterday approved sending Congress a $1.6 billion appropriations request for fiscal 1981. Postal officials estimate a $19 billion budge for fiscal 1981, 2.9 percent more than the previous year, with a $2 billion deficit if a postal rate increase is not approved for that year.

"If you want to keep the rate schedule the same, the taxpayers will have to cough up from taxes 2.384 billion more dollars," Bolger told the governors. t

Last week Bolger announced that the postal service had a $470 million surplus for fiscal 1979, marking the first time since the end of World War II that the postal system operated without a loss for an entire fiscal year. At that time Bolger said that he didn't anticipate any postal increase before 1980. A spokesman said yesterday it is too early to file for a rate increase for 1981.