The efficiency experts at Treasury have managed to clog up the phone lines at the Department's Bureau of the Public Debt.

The problem began last year when the department tried to consolidate the tax statements it sends to holders of notes, bonds and bills telling them the amount of interest they earned during the year.

The idea was to give each holder only one statement instead of separate statements for each security.

But it didn't work out quite the way it was planned.

It seems that 12,000 holders of a particular government note had their earnings counted twice on the new single form.

As a result, many of the owners of a two-year, 9 7/8 U-85 note that matures May 31, 1985, have been lighting up the Treasury switchboard wanting to know what happened.

How many calls? "Too many. A great deal, believe me," said one harried analyst.

Treasury spokesman Brien Benson said the correct figures were sent to the Internal Revenue Service and notices have been mailed to holders of the notes explaining the mix-up.

No other securities were involved, he said.

"We mailed out 807,000 statements, and this is a tiny fraction of them," Benson said.

"I think it's a tribute that the new system worked this well," he added. "You're talking about a lot of stuff going out."