LONDON (AP) _ Share prices on the London stock exchange were mixed in lackluster trading at midday today, as the market drifted without direction.

At about 12:30 p.m., the Financial Times-Stock Exchange 100-stock index was down 3.8 points at 1,647.8. The index opened 0.6 points up at 9 a.m., its high for the day, and then drifted to its low of 10.4 points down at 9:31 a.m. before recovering.

At noon, volume totaled a sparse 199 million shares, compared with 379.8 million shares at the same time Friday.

Dealers said the weaker dollar was hurting some major shares, while selective buying was helping others.

Dealers said British economic data released today was in line with expectations and had little impact on the market. ''With the lack of trade, we're just going to keep drifting,'' said one dealer.