RICHMOND, JAN. 19 -- Rep. W.C. (Dan) Daniel, the conservative Democrat who has represented Virginia's Southside region in Congress for 19 years, said today he will not seek reelection this fall because of heart trouble.

The announcement by the 73-year-old Daniel, a craggy, white-haired Chatham native whose politics sprang from the rural, largely white region where he built his career, is likely to touch off a scramble for his 5th District seat among several Democrats, including a handful of state legislators, according to observers here.

As word of Daniel's decision spread through the Capitol where the General Assembly is in session, some party leaders were touting state Sen. Virgil H. Goode Jr., 41, a Rocky Mount Democrat known here and back home for his fiery, florid oratory.

Also contemplating a run for Daniel's seat is state Senate Clerk J.T. Shropshire, 42, now embroiled in a nasty public dispute with some of his Democratic masters in the legislature's upper chamber.

Several Democrats of the House of Delegates, where Daniel once represented the City of Danville, also were reported to be considering running; a Southside welding shop owner already had announced that he would challenge Daniel for the Democratic nomination.

Daniel, who was hospitalized several times last year, entered the University of Virginia Medical Center today as an outpatient for further tests. At the same time, he issued a statement announcing that he was unable to give a "100 percent effort" in office and would retire.

"There are times when the pace is not easy," Daniel said of the regimen in Congress.

Daniel, a ranking member of the House Armed Services Committee, embodied the ideals of the Byrd organization that once dominated Virginia and brought him along in politics. A former state Chamber of Commerce president and national commander of the American Legion, he voted on budget and defense issues as a conservative first, a Democrat second.

Linda Arey, a lawyer and teacher who has held political posts in the Reagan administration, announced last week that the she would seek the Republican nomination for Daniel's seat.