The Food and Drug Administration last week doubled the fee it charges for certifying the purity and potency of the insulin used by up to 1.7 million diabetics in this country.

David Petak, an FDA accountant, said proliferation of new methods for manufacturing insulin--including new gene-splicing techniques--has forced the agency to increase its inspection staff from 10 to 16 people. FDA expenditures for inspection and certification have increased from $400,000 to $900,000 in two years, Petak said.

FDA also cited increased support costs for the testing program, which used to share such costs with a now-defunct antibiotic testing program. FDA ended that program last year, saying it was no longer necessary in light of improvements in manufacturing practices.

The agency last year certified 4.8 million vials of insulin, which retail for about $6. Before the new fees went into effect, Petak estimated, the certification process cost manufacturers less than a penny per vial--a cost that will go up to about 2 cents per vial under the new fee schedule. A vial provides a diabetic with enough insulin for 10 days to two weeks, he said.

Officials of Eli Lilly & Co., the pharmaceutical firm that manufactures most of the insulin on the market, declined to comment on the fee increase, saying they wanted more time to study the document.

FDA put the fee increase into effect in a final rule in Friday's Federal Register, without going though the normal process of notice and comment. --Cass Peterson and Felicity Barringer