A last-minute surge of more than 5,000 registrants yesterday -- on the final day to sign up to vote in the District's Sept. 14 primary elections -- was expected to push the total number of eligible voters over the 300,000 mark, elections officials said.

The count on Sunday was 294,922 voters. Officials said the final tally would not be known for several days because applications postmarked by midnight yesterday will be counted if they are received within six days. The total registration count in previous years has been about 280,000.

With 28 days remaining before the primaries, the elections office is still working to sort out longstanding problems centering on record-keeping.

Last spring, a City Council committee said the ballots of more than 50,000 people could be jeopardized in September because of inaccurate, missing or incomplete data.

Teddy Filosofos, a Buffalo, N.Y., elections official hired last May to bring order to the city's records, said yesterday that many of the problems have been solved and that he expected the elections to go smoothly.

In another action yesterday, the D.C. Board of Elections and Ethics turned down an appeal by mayoral candidate Morris Harper to place his name on the ballot.

The board ruled recently that Harper had not filed the required number of 2,000 valid signatures of registered Democrats. A board official said yesterday that Harper had submitted 2,418 signatures, but that only 1,175 of them were of properly registered persons.

The board also reversed a ruling it made last week and certified Republican John West as a candidate in the race for D. C. delegate.