MidAtlantic Trust Company said it had resolved record-keeping problems that have kept exchange-traded funds from being part of holdings in 401(k) and other retirement plans.

The state-chartered trust company said it has resolved a problem with fractional shares that result from trading in ETFs that have kept such funds from being kept in retirement plans. The firm said it will buy and sell whole shares in the market and hold fractional shares as necessary. This will allow “dollar certain” transactions that until this have prevented the information systems that keep track of funds from recognizing and tracking ETF shares.

Shares will be bought at end-of-day prices, allowing same-day settlement for record-keeping purposes. Mutual funds historically have determined the value of their assets at the end of each trading day, for their investors. ETFs, however, follow the three-day settlement cycle of equities markets.

In postings to its Web site, MidAtlantic said this will “allow record keepers the ability to handle ETFs using the same systems and processes they already have in place for trading mutual funds.’’

Roughly $13 trillion are held in the United States in mutual funds, which surged in popularity in the ‘80s and ‘90s. At the end of 2012, $1.3 trillion was held in the U.S. in ETFs, which got started 20 years ago by State Street Corporation. The ability to trade shares in the funds as if they were shares of stock has made them an increasingly significant part of equities trading on national exchanges. In 2012, exchange-traded products accounted for 14.3% of all trading on stock markets in the United States.

A technology unit of the company, Mid Atlantic Financial Platforms, has introduced what it calls the ETFxChange, to resolve the record-keeping issues and spur their use in retirement plans.

Shares of ETFs from BlackRock’s family of iShares products, as well as ETFs from PowerShares, Wisdom Tree, State Street and Vanguard also can be handled by the system. Stadion Money Management in Watkinsville, Ga., confirmed that it will use the platform on behalf of its customers.

MidAtlantic also launched a related ModelxChange that allows money managers, investment advisors and plan record-keepers to create and maintain investsing models for 401(k) plans that mix ETFs with mutual funds.