A massive MCI Communications Corp. advertising blitz got into full swing yesterday in Denver, but residents of that mountain city ran into a problem in getting information on the company's new residential telephone service program.

For at least several hours, Denver residents could not get through to MCI sales representatives there. The MCI telephones, supplied by the Bell System, were not functioning properly.

The problem, called a central office technical foul-up with the computer system, touched off a flurry of calls to AT&T's subsidiary, Mountain Bell Telephone Co., in Denver and added to tension between rivals MIC and AT&T.

MCI has launched a program in Denver and several other cities designed to pickup its first share of the residential market. Yesterday the program resulted in full-page ads in Denver newspapers.

MCI officials, who say the response to the program has been better than expected threatened AT&T with further legal action -- MIC has already hit AT&T with a $2.7 billion antitrust suit in Chicago -- if phone system hook-ups with MCI in Denver are not functioning properly.

"It's been in and out all this week," said Jerry Taylor, an MCI vice president. "The lines have been dead, they've been up and they've been down." p

MCI Chairman William McGowan, who said company attorneys had arrived in Denver to take depositions on the problem and would consider going to federal court to get a restraining order, was outraged at the situation.

"I thought somebody was pulling my leg," McGowan said of his reaction to the news. "This is just ridiculous. Lord knows how many customers we've lost."

Ted Sandquist, a public relations official with Moutain Bell Telephone, said the company is committed to "giving MCI good service," Sandquist called the problem a "human error in reprogramming."

"As part of the reprogramming of our computer, we were putting that order activity into the computer," he explained. "There were 40 modules that had to be completed. On the fourtieth and final process change, our technician made a mistake."

Sandquist said the error affected a wide area of calls and said the company had received 116 "trouble reports" from the vicinity.

Calls to MCI's Denver sales office early yesterday were answered by a recording saying the number was no longer in service, Sandquist said the problems were cleard up by 9:30 a.m.. Denver time.

MCI officials also said the Bell System operators had given some callers the number of the MCI computer terminal in Denver, a charge denied by the Bell spokesman. "If an individual oprator did that, it was against company policy," Sanquist said, "Our directory assistance operators are not giving that number out."

But MCI officials also said that Denver users of their business telephone or "Execunet" service had also lost service, as had Honeywell Inc. tclients of MCIthere. AT&T officials could not explain those system failures.

An AT&T spokesman here, Pic Wagner, said MCI officials "should know better than that" referring to the implicit charge that AT&T was out to gut the MCI effort.

"If MCI is charging that we are trying to affect this service, it is absolute nonsense" Wagner said.