What once looked like a classic snapback rally had completely fallen apart by midsession.

The

Nasdaq Composite Index

cracked back through the 5000 barrier shortly after trading began, and managed to hold much of its early strength until about a half hour before noon, when selling started to pick up. The Comp was lately down 58, or 1.2%, to 4849, with big-cap component

3Com

(COMS)

off 10.1% and biotech big'un

Amgen

(AMGN) - Get Report

down 5.2%.

The action in Amgen was symptomatic of the biotechnology sector in general, where the recent consolidation in a wide range of stocks was accelerating to an absolutely screaming pace. Check the damage on the darlings:

Protein Design Laboratories

(PDLI) - Get Report

, down a staggering 57 7/8, or 22.5%, to 199;

Immunex

(IMNX)

, off 14 3/4, or 8%, to 170 5/8;

Millennium Pharmaceuticals

(MLNM)

, down 38 3/4, or 16.5%, to 196 3/4.

Blame

President Clinton

and U.K. Prime Minister

Tony Blair

, whose pledge today to democratize data from the

Human Genome Project

for the benefit of science seems to have set off an all-out panic.

"It's very indiscriminate," said Sven Bohro, money manager at

Orbimed Advisors

. "Any thing related to genomics is selling off."

Blair and Clinton said in a statement: "To realize the full promise of this research, raw fundamental data on the human genome, including the human DNA sequence and its variations, should be made freely available to scientists everywhere."

Gene mapper

Celera Genomics

(CRA)

, which hopes to patent its data on human genes research, was down 52 1/2, or 28%, to 136 1/1.

The severity of the market's reaction to those words might seem a bit excessive. But all moves, whether up or down, make sense in a hard-core momentum sector. "What was driving the upside is now driving on the downside," Bohro said. "All the momentum investors and retail guys who have been running up this sector are scared s---less. They're running for the exits."

Days like this don't do much for sentiment. While the general mood on desks wasn't necessarily panicky, traders were hardly relaxed. "It seems like there's a lot of doomsday scenarios circulating," said Paul McEnroe, trader at

TheStreet Recommends

Brown Brothers Harriman

. "So there is some sense of nervousness. But the same thing can be said now that was said 1000 points ago on the Nasdaq."

"But you can't help but feel as though it's a bubble," McEnroe continued.

Things were looking quite a bit better for the broader market. The

S&P 500

was down 4, or 0.3%, to 1379, while the

Dow Jones Industrial Average

was off a fraction to 9946 1/2. Dow component

Alcoa

(AA) - Get Report

plummeting 6.4% after agreeing to buy aerospace industry supplier

Cordant Technologies

(CDD)

for $57 a share. Cordant, predictably, was flying on the news, up 87.5% to 55 7/16.

Internet stocks were mixed, with the upside exception of

Inktomi

(INKT)

, which was up 11.1% after unveiling six alliances to enter the mobile wireless market. But

CheckPoint Software

(CHKP) - Get Report

was down 35 3/16, or 13.1%, to 233.

A Treasury

buyback announcement was helping the bond market edge higher, with the benchmark 10-year note up 11/32 to 101 9/32, putting its yield at 6.323%. Bondsmen (and -women) weren't unduly bothered by this morning's

news that retail sales grew 1.1% in the month of February.

Banks and brokerages were also seeing mixed action. The

American Stock Exchange Broker/Dealer Index

was up 1.2%, while the

Philadelphia Stock Exchange/KBW Bank Index

was 0.3% higher.

Small-caps were getting hit hard, with the

Russell 2000

down 8 1/2, or 1.4%, to 582.

Market Internals

Breadth was negative on strong volume.

New York Stock Exchange:

1,355 advancers, 1,468 decliners, 658 million shares. 32 new 52-week highs, 93 new lows.

Nasdaq Stock Market:

1,644 advancers, 2,406 decliners, 1.2 billion shares. 154 new highs, 67 new lows.

For a look at stocks in the midsession news, see Midday Movers, published separately.