Alexandria Del. Richard R. G. Hobson said yesterday he will not seek reelection to the Virginia House of Delegates where he has served for the last four years.

The surprise announcement by the 47-year-old lawyer, a Democrat, followed by just a few days a similar announcement by Del. Gary R. Myers (R-Alexandria) and left the city without either of its two incumbent delegates running for office again in the General Assembly's 21st District.

"I had sort of hoped I was going to run again and I expected to," Hobson said after the election withdrawal statement was issued by his office. "But when I got back [from the 1979 legislative session in Richmond] and looked at the practicalities of life" he changed his mind, he said.

Hobson said the General Assembly's increasing demands on his time were hurting his law practice.

"I never intended to make a career out of the House of Delegates," he said. But Hobson emphasized that "I'm not going away" and said he planned to stay active in the Democratic Party at the state and local level "in finding and encouraging persons of integrity and ability to seek and hold public office."

Hobson said the decision by Myers, who ousted former House Majority Leader James M. Thomson nearly two years ago, was not a factor in his own decision to quit the Assembly. Hobson led the successful fight in the legislature last year against Thomson's nomination as a Circuit Court judge for the city.

State Sen. Wiley F. Mitchell Jr. (R-Alexandria) plans to seek a second term, but Hobson said there is no way of speculating at this point who some of the other Assembly candidates will be in the June 12 primary. Deadline for filing by party designation is April 13. The general election will be held Nov. 6.