f the secretary of defense lunches downtown with a four-star general or admiral, who should pick up the check? Well, if you go by disposable income,the military man might want to do the honors.

The General Accounting Office says in a new study that military personnel have 7 to 10 percent more in actual income after deductions than their civilian counterparts and some of their bosses in government -- even where civilians have higher salaries.

The fascinating report, prepared for the Senate Armed Services Committee, is sure to cause some tension in the rank-conscious Pentagon, which is chock-full of high-grade civilian and military personnel.

GAO took a look at salaries and taxes and other deductions -- and came up with an equation figuring in a varying number of dependents -- and concluded that, in general, military personnel have more take-home income at every level than federal workers.

GAO cited a number of reasons for this, including the fact that federal workers must contribute 7 percent of their salaries toward retirement, and pay for health insurance plans that are free to the military. In addition, GAO said, portions of military compensation, such as subsistence and housing allowances, are not taxed.

Here are some examples of the report's findings:

* A top-ranking general or admiral is paid $88,839 a year, compared with $88,200 for a cabinet officer. But the GAO figures that the military person ends up with $56,974 in disposable income (or 64.1 percent) compared with $49,375, or 57.3 percent, for the secretary of defense.

* The annual salary of a brigadier general or commodore is $78,753, and of that amount $52,146 is disposable income, the GAO said. For a subcabinet officer or head of an independent agency, the breakdown is $75,100 in salary, and $44,353 in disposable income.

* An Army or Air Force lieutenant colonel or Navy commander is paid $57,662 a year and has a disposable income of $40,600. Their civilian counterparts -- members of the Senior Executive Service -- earn $61,296 at SES's lowest pay level and have estimated disposable incomes of $37,893, GAO says.

* Sergeants major and master chief petty officers earn $42,116 a year, with disposable incomes of $31,944. GAO says that a Grade 14 civil servant earning nearly $6,000 more in gross salary has disposable income of $31,629.

* A civil servant in the fourth step of Grade 12 is said to earn $34,781 and takes home $23,733. A sergeant first class or chief petty officer earning $30,177 would have a disposable income of $24,508.

* At the first step of Grade 5 ($14,390 a year) the disposable income of a civil servant is $10,283, or 71 1/2 percent of salary. A private first class or seaman earning $15,516 would have 82.4 percent, or $12,786 in disposable income, according to the GAO report.

For purposes of the study, the GAO figured take-home pay using Virginia income taxes. But many military personnel, especially those in the higher ranks, actually have more disposable income because they legally claim residence in states that do not have income taxes, or do not tax military income.

Both civilian and military pay experts caution, however, that the GAO tables are not a true measure of comparable worth. They note that the GAO rankings do not measure the value of other aspects of service -- from retirement benefits to the cost of moving or the trauma of combat. But the comparisons will probably be good enough to start a few arguments.