NEW YORK (AP) _ Drexel Burnham Lambert Inc.'s historic plea-bargain deal with federal prosecutors has had little effect on the financial markets.

News of the settlement of fraud charges caused nary a ripple Thursday even in Drexel's own backyard, the market for high-risk, high-yield ''junk bonds,'' which the investment firm pioneered.

Conventional bonds as well as stocks also failed to register a reaction.

The Dow Jones average of 30 industrials slipped 4.28 points to 2,160.36 Thursday.

A ''flight to quality'' out of junk bonds and into conventional securities, which had been predicted in some quarters as a result of the Drexel debacle, failed to materialize.

Treasury, corporate and municipal bonds had an uneventful trading day, finishing mixed. The yield on the Treasury's closely watched 30-year bond slipped to 8.93 percent from 8.94 percent late Wednesday.

U.S. Attorney Rudolph W. Giuliani announced late Wednesday, after the markets closed, that Drexel had reversed itself by agreeing to admit guilt to six felonies and pay a record $650 million fine to settle the biggest securities fraud case in history.

Expectations of a Drexel settlement had grown in recent days, and the markets weren't taken by surprise. In fact, they seemed relieved that the business was over with and Drexel had decided not to wage a risky fight.

''This one's been hanging around for some time,'' said Monte Gordon, director of research at Dreyfus Corp.

All the markets were quiet, at any rate, as trading slowed in anticipation of the Christmas and New Year's holidays.

''The only surprise is that (the Drexel settlement) happened on Wednesday,'' said Micheal Metz, a stock market analyst for Oppenheimer & Co. ''At least for the moment, Drexel is still in the arena and functioning.''

Wall Street had already shown some support Wednesday for an anticipated settlement, by lifting share prices of RJR Nabisco Inc., Polaroid Corp. and a few other takeover-related companies. Junk bonds are widely used to finance debt-financed takeovers of companies.

The takeover stocks have been buoying the otherwise lackluster market in recent weeks.

Without the boost provided by those stocks, ''we've got no performance at all, period,'' said Oppenheimer's Metz.