By Svea Herbst-Bayliss

NEW YORK, Nov 14 (Reuters) - Activist investor Jana Partners liquidated two positions it built earlier this year where it did not press for changes and dramatically downsized its stake in a third company where it pushed for a sale that was announced in September.

In its quarterly 13-F filing on Thursday, the hedge fund said that it had sold 5.7 million shares in Frontier Communications during the third quarter, cutting its position by 59%.

A day earlier, Frontier Communications shareholders agreed to sell the company to Verizon in a $20 billion deal, including debt, that is expected to strengthen Verizon's fiber network.

Jana first publicly pushed Frontier to put itself up for sale a year ago.

Frontier's stock price has climbed 67.5% in the last 52 weeks and spiked in early September when the Verizon deal was announced.

The hedge fund also exited its position in U.S. diagnostics company QuidelOrtho , which it built during the first quarter, and its position in enterprise software company BlackLine Systems , which it built during the second quarter.

It was unclear earlier in the year whether Jana would seek changes at these companies and in the end, the hedge fund did not mount public campaigns.

Jana is currently pushing cybersecurity company Rapid7 to sell itself and has increased its holding by 34.2% to 3.7 million.

Investors are required to make the so-called 13-F filings with the U.S. Securities and Exchange Commission to show what they owned in U.S. companies' stock at the end of the quarter.

While the filings are backward looking, they are closely tracked for hints on which companies activist investors may target.

(Reporting by Svea Herbst-Bayliss Editing by Marguerita Choy)

((svea.herbst@thomsonreuters.com; +617 233 2138; Reuters Messaging: svea.herbst.thomsonreuters.com@reuters.net))