The Boeing Co. enjoying a boom in sales of jetliners, yesterday reported third quarter earnings more than double last year's and declared a special dividend.

The aerospace giant, reporting nine months sales of $3.8 billion and earnings of $215.3 million or $5.05 per share, declared a regular dividend of 30 cents per share and a special dividend of 50 cents per share, payable Dec. 11.

In 1977, the nine-month earnings were $124.5 million or $2.93 per share on sales of $2.9 billion.

This year's third quarter earnings were reported at 92.6 million compared with $39.9 million in the third quarter of 1977.

T. A. Wilson, chairman, told the board of directors, that improved earnings were attributable to increased sales volume, continued favorable performance on major programs, the impact of increasing commercial jet transport production rates and other increased income.

Loew's Corp. earned $2.93 a share in a third quarter, including 22 cents from realized investment gains, up from $2.17 a year ago, when realized investment gains were 81 cents a share.

Revenues rose to $877.29 million from $848.68 million

Loew's nine months profit was $7.43 a share, including realized investment gains of $1.06, against $7.90 a share a year earlier, which included realized investment gains of $2.21 a share and $2.39 a share in income from operations since discontinued. Net income was $10.73 million on revenues of $2.535 billion compared with $11.17 million on revenues of $2.39 billion.

Loew's stake in CNA Financial Corp contributed about 44 percent of the 1978 third quarter profit compared with 55 percent a year earlier.