Just compiled voter registration figures appear to underscore the necessity for Democrat Henry E. Howell to win by big margins in his Tidewater base if he is to become Virginia's next governor.

Although the figures tend to show what state election officials call unusually light registration statewide, what registration has occurred appears to have been concentrated in areas considered by most politicans to be favorable to Howell's opponent, Republican Lt. Gov. John N. Dalton.

By comparison, four of the six Norfolk area cities that have provided the base for Howell's two previous races for governor showed comparatively little new voter registration. The result, according to some knowledgeable politicans here, could make Howell's Norfolk base even more crucial to him in the Nov. 8 election.

Howell's strategists had hoped to build this base immediately after the June 14 Democratic primary, but because of money problems that have nagged Howell's campaign from the outset, were unable to mount such a drive. "We went ahead with a drive to the extent we could," said Howell's state manager William Rosendahl, but he said the drive was limited.

Dalton's supporters never planned a registration drive, but William A. Royall, Dalton's state manager, was unable to conceal his delight over the comparatively high registration the new figures show in the Richmond area. Richmond and its conservative suburbs have traditionally been one of Howell's weakest areas in the state.

Overall the state figures show a net gain of 1.8 per cent in voter registration since Dec. 31 when 147,000 persons who had not voted in the four previous years were purged from the state's rolls. The increase to the present total of 2,020,623 voters, however, is nowhere near the 6.9 per cent increase in registrations the state had prior to the 1976 presidential election.

In fact, the current state total is well below the 2.1 million voters Virginia had a year ago. The decrease appears to result from extensive voter registration purges of people who have left the traditionally transient areas of Northern Virginia and Norfolk, according to state elections officials.

No place in the state has experienced as large an increase in new voters as has the southwest Virginia town of Radford, Dalton's home. According to state figures, the town has had a net gain of 340 voters, or 7.2 per cent more voters than it had at the first of the year.

Dalton on the campaign trail regularly tells audiences of a 105-year-old evangelist known to his staff only as "Rev. Bealsey," who was talked into registering in Radford by Dalton's mother. Royall said she is largely responsible for the increase to 5,065 voters in Radford.

Norfolk, the state's largest city and Howell's hometown has had a net gain of only 715 voters since Jan. 1 and the net gains in Portsmouth, Virginia Beach and Chesapeake also have been small. Newport News and Hampton, two other cities in Howell's base, did have a net gain of 2,510 voters.

In Richmond itself, which Howell carried by a 52 per cent margin in his 1973 race against Gov. Mills E. Godwin, there has been a net gain of 4,952 voters this year.

But in adjacent conservative Henrico and Chesterfield Counties there was an offsetting gain of 4,986 voters this year. Royall said the relatively high registration in the Richmond area is a product of "just the strong anti-Henry sentiment" here. Polls show that "no where in the state is there as much anti-Henry as there is "in the Richmond area" Royall said. "You can run anybody against Henry and the opponent will get a majority of the votes here."

Northern Virginia's number of voters declined sharply after the yearend purge. But most jurisdictions have shown modest gains since the first of the year. The current number of qualified voters followed by the number (in parentheses) at the start of the year are: Fairfax County, 253,935 (238.061), Alexandria, 44,796 (43,805); Arlington, 76,799 (74,282); Prince William, 35,538 (34,921); Loudoun, 20,863 (20,469); Fairfax City 9,290 (9,025) and Falls Church 4,963 (4,984).