In an effort to increase tax collections by $3 billion in fiscal year 1982, the Reagan administration is exploring seven major changes that would increase tax liabilities for a variety of groups including contractors, persons collecting unemployment benefits and subsidiaries of life insurance companies.

The administration, carefully attempting to avoid any implication that it would raise taxes, described the proposals as an effort to "curtail certain tax abuses and enhance tax revenues." The proposals are still in the tentative stage, but they include:

* Taxation of business income from contracts. Current law requires payment of taxes upon completion of a contract. The administration is considering speeding up the tax collection process so that taxes would be owed as partial payments are made on the contract. The change would be particularly significant for major defense contractors working on long-range projects.

* Energy tax credits. The administration is considering lowering or eliminating the tax credits available to individuals and businesses using solar and other energy sources that do not depend on oil or gas.

*5Industrial development bonds. The administration, following the lead of many members of Congress, is considering placing restrictions on the use of tax exempt industrial development bonds. At present, the exemption is being used by developers of tennis courts, fast food chains and other activities that a number of public officials contend do not need tax support.

* Life insurance. Under a loophole in current law, subsidiaries of life insurance companies that co-insure clients together with the parent company are able to halve their tax liabilities. Income from investments, which is taxed at a rate of 40 percent, can be converted to underwriting income under the law which reduces the tax rate to 23 percent or less.

* Unemployment compensation. Current law permits persons collecting unemployment compensation to avoid taxation on the payments as long as their total income for the year is less than $20,000 on a single return and $25,000 on a joint return. Lowering these ceilings would significantly increase tax revenues. According to one estimate, if the ceilings were lowered to $10,000 for a single return and to $15,000 for a joint return, the revenues would exceed $1 billion.

* Corporate tax collections. The recently passed tax reduction bill included language requiring companies with income exceeding $1 million in any of three past years to increase the size of quarterly payments. The administration is considering methods of accelerating these payments.

* Administative changes. The Treasury Department is attempting to come up with a series of methods to improve tax collection and enforcement procedures used by the Internal Revenue Service. Some of these changes are expected to focus on what is known as "the underground economy" where exchanges are made in services and cash in an effort to avoid taxation.

A Treasury Department spokesman emphasized that these are areas under consideration, and new proposals may be added to the list. He said present calculations are that at least $3 billion could be raised from these proposals.