The Senate sent legislation to the White House yesterday that would authorize payment of 1985 health insurance refunds to most federal workers and retirees, including more than 250,000 here.

President Reagan is expected to sign the bill, which would give a major part of the $1 billion refund to the government. It also contains a provision that is expected to lower health premiums next year for many persons who signed up for low-cost health insurance plans. The premium cuts for them would take effect in March or April.

Nationwide, about 2 million civil servants and retirees are due the rebates, which are expected to range from $18 to $400 per subscriber. Checks will probably be sent out next month.

The size of refunds depends on the plans employes or retirees were enrolled in this year and whether they paid high-option or standard (low-option) premiums. Postal workers and retirees will get smaller refunds than other federal workers because the U.S. Postal Service pays a bigger share of their insurance premiums.

A number of major plans in the federal health program proposed the refunds this year after a government-ordered cutback in financial reserves of the health program.

Blue Cross-Blue Shield, the largest health plan, said the primary cause for the buildup in reserves was that workers and retirees weren't using their insurance as much, or were paying a bigger share of their own medical bills. The Reagan administration approved of the refunds, but Congress had to pass special legislation to allow retirees to get them.

Most of the plans participating in the federal health program balked at the idea of giving refunds, but nearly all of them cut their premiums substantially, although some have warned that premiums are bound to go up dramatically in 1987.

Plans offering refunds (only to 1985 policyholders) include the Foreign Service Plan, Aetna, the Government Employees Hospital Association, Government Employees Benefit Association, American Federation of Government Employees, National Association of Letter Carriers and Blue Cross-Blue Shield.