NEW YORK, JUNE 19 -- The stock market forged ahead today, extending its advance to record highs as Wall Street experimented with new procedures designed to smooth out the quarterly "triple witching hour."

The Dow Jones average of 30 industrials rose 12.72 to 2420.85, bringing its gain for the week to 43.12 points.

Volume on the New York Stock Exchange reached 220.48 million shares, up from 168.58 million Thursday.

There was a burst of activity at the outset as positions were settled by traders in stocks covered by the June futures contract on Standard & Poor's 500-stock composite index. It was the first time that contract and a few other stock-index futures and options were settled as of the opening on expiration Friday instead of on the close.

The new procedure appeared to go smoothly, with no dramatic price swings in the market. However, some analysts said many professional traders who might otherwise be active had stayed clear of the market because of uncertainty about how trading would go.

A second settlement period at the close for several other stock-index contracts went just as uneventfully, enabling the market to close its fourth straight week of gains on a strong note.

Thus, the storms that some observers feared might accompany the first "double triple witching hour" didn't materialize. As one observation that made the rounds of the Big Board put it: "Double, double, toil, no trouble."

Merck was the biggest contributor to the Dow industrial average's gain, rising 3 3/8 to 165 3/4 on interest in a cholesterol-reducing drug being developed by the company.

Among the other blue chips, International Business Machines rose 1/2 to 161 3/8; International Paper 1 3/8 to 49 1/2; Exxon 1/4 to 90 1/8, Coca-Cola 3/4 to 45 3/8. American Telephone & Telegraph, unchanged at 28 7/8, led the active list on turnover of more than 5 million shares.

Electrospace Systems dropped 3 3/8 to 26 3/4 after word that Chrysler agreed to acquire the company for $27 a share, a lower price than some traders had expected. Chrysler was up 1/4 at 35 7/8.

National Semiconductor rose 3/4 to 13 5/8. The company reported operating earnings of $3.9 million for the quarter ended May 31, against an operating loss in the comparable period a year earlier.

Advancing issues outnumbered declines by more than 3 to 2 on the NYSE. The exchange's composite index gained 0.73 to 172.57.