FINANCIAL MARKETS : 30-Year Bond Yield Falls Below 6%; Stocks Mixed : Markets: Treasury bond figure, lowest in more than 2 years, reflects confidence that low inflation, interest rates will persist.

Yields on 30-year Treasury bonds were below 6% at the end of Thursday’s session, the lowest level in 26 months, as traders continued to be confident of low inflation and interest rates next year.

Stocks ended mixed, with computer-related shares taking a tumble after a semiconductor maker warned of disappointing earnings.

The bellwether treasury bond’s closing yield of 5.98% was its lowest since Oct. 29, 1993, when the 30-year yield finished at 5.97%. The yield had slipped below 6% briefly before the close Wednesday.

But analysts said thin trading made the market’s move more pronounced than it might otherwise have been.

“Many places, including ours, have moderate-sized trading crews right now,” said Michael Moran, chief economist at Daiwa Securities America Inc. He noted that in the absence of government-collected data, the market is moving on reports to which it might otherwise pay less attention.

“The last time it touched these levels, it quickly backed off,” Moran said.

The Conference Board reported Thursday that its help-wanted advertising index slipped to 127 in November from 131 in October, indicating weakness in the job market. Separately, the New York arm of the National Assn. of Purchasing Management reported that growth in that region slowed in December.

The data helped bond prices because they point to lower inflation and lower interest rates as the economy slows. Inflation is a bond investors’ worst enemy, as it erodes the value of the returns bonds pay.

Short-term interest rates fell a few hundredths of a percentage point. Three-month bill rates fell to 4.85%. Six-month bill rates dropped to 4.90%.

The two-year note edged higher to yield 5.20%.

In equity markets, the Dow Jones industrial average ended down 10.12 points at 5,095.80.

Despite the loss in the blue-chip index, advancing issues had a slight lead of 8 to 7 on decliners on the New York Stock Exchange. Volume exceeded Wednesday’s pace but remained light at 288.48 million shares as of 4 p.m. Many investors are sidelined during the week between Christmas and New Year’s.

Broad market indexes were mostly lower, pressured by computer shares. The NYSE composite index rose 0.22 point to 328.35. But the Standard & Poor’s 500-stock index fell 0.41 point to 614.12, the Nasdaq composite index fell 5.91 points to 1,042.22, and the American Stock Exchange market value index fell 0.18 point to 544.52.

Stocks were under pressure as investors sold holdings to book profits before the year ends. Analysts said that one logical sector in which to take profits is technology, because it has performed so well this year.

Technology stocks were sold aggressively after Cirrus Logic, a computer chip maker, warned late Wednesday that its third-quarter earnings would be between 13 cents and 19 cents a share, far short of consensus estimates of 44 cents. Cirrus shares skidded 7 points to 19 7/8

The Fremont, Calif., company blamed slow sales of home personal computers and softer business conditions in Taiwan.

Analysts said the traditional “Santa Claus rally” remains somewhat elusive on Wall Street, adding that the lack of one could be a warning for 1996. “As the old saying goes, ‘If Santa should fail to call, bears could come to Broad and Wall,’ ” said Frank Gretz, a technical analyst at Shields & Co.

But Tony Dwyer, chief market strategist at Josephthal Lyon & Ross, said: “Just because the market doesn’t rally in the last five sessions of the year doesn’t mean it’ll be a bad year. I see the market up [next year] because of low inflation, low interest rates and a moderate-growth economy, which should translate into solid corporate profit growth.”

Among market highlights:

* Cirrus dragged other computer-related shares with it. Intel fell 1 3/4 to 57 1/8, Cisco Systems lost 3/8 to 75 3/8, Oracle slid 1 1/8 to 42 3/8 and Sun Microsystems slumped 2 to 44 3/8. IBM, which lost 7/8 to 90 1/8, led the Dow industrials lower. Compaq declined 2 to 46 3/4.

* Utah Medical Products jumped 5 3/8 to 20 5/8 after winning Food and Drug Administration approval to market its Cordguard II device, used to clamp and cut the umbilical cord to acquire uncontaminated blood samples after birth.

* Tekelec tumbled 5 1/2 points to 10 1/4 a day after the maker of telecommunications test equipment warned that its fourth-quarter earnings would fall below forecasts. Alex Brown cut its recommendation for the stock to “neutral” from “strong buy.”

* Philip Morris fell 7/8 to 89 7/8. The Wall Street Journal reported that cigarette makers are likely to face new rules restricting their advertising and marketing practices. The Federal Trade Commission is seeking to require the companies to show a wide range of tar and nicotine levels in cigarettes ads, the paper said.