When a majority of troops told the Pentagon this summer they didn’t care if gays were allowed to serve openly in the military, it was in sharp contrast to the time when America’s fighting forces voiced bitter opposition to accepting racial minorities and women in the services.

The survey, due out Tuesday, is expected to find pockets of resistance among combat troops to ending the ban on gays. Some 70 percent of respondents were expected to say that lifting the ban would have a positive or mixed effect, or none at all, according to officials familiar with the findings.

The study is expected to set the stage for a showdown in the Senate between advocates of repealing the 17-year-old “don’t ask, don’t tell” law and a small but powerful group of foes in the final days of the lame-duck Congress.

Repeal would mean that, for the first time in U.S. history, gays would be openly accepted by the military and could acknowledge their sexual orientation without fear of being kicked out.

U.S. troops haven’t always been so accepting. Troop surveys conducted throughout the 1940s on blacks and Jews, and in the 1970s and 1980s on women, exposed deep rifts within a military that was dominated by white males but becoming increasingly reliant on minorities to help do its job.

In a study from July 1947, four of five enlisted men told the Army that they would oppose blacks serving in their units even if whites and blacks didn’t share housing or food facilities.

The same study also revealed a deep resentment toward Jews. Most enlisted men said Jews had profited greatly from the war and many doubted that Jews had suffered under Adolf Hitler.

“Negro outfits should be maintained separately,” an Army master sergeant from North Carolina told the Pentagon in 1947. “To do otherwise is to invite trouble and many complications. The equal rights plan should not be forced on the Army as an example to civilians.”

Troops also offered dire predictions for what would happen if whites and black units were forced to serve together.

“For sure, all the GIs will quit the Army or buck like hell to get out,” a 20-year-old Army private first class told the surveyors. The service members were quoted anonymously in the 1947 study.

Added another 19-year-old soldier: “If the Negro and the whites were mixed, there would be a civil war among the troops. There would be a lot of useless bloodshed if this happens.”

President Harry S. Truman issued a 1948 order on equal treatment of blacks in the services anyway, paving the way for integration during the Korean War. None of these doomsday scenarios came true.

It wasn’t until Vietnam, when racial tensions in the civilian world bubbled over into the military, did race riots erupt in all four military branches.

By the 1980s, the military faced the issue of whether to allow women to serve on Navy ships and elsewhere on the battlefield. Troops were generally much more open to serving with women than they had been to serving with African-Americans 40 years prior. Still, many expressed serious concerns that allowing females as crew members would cause problems.

In one 1981 study, lower-ranking enlisted sailors blamed female crew members for a decline in “discipline, leadership and supervision.”

As was the case in racial integration, letting women serve aboard ships and, eventually, on combat aircraft, didn’t always go smoothly.

In 1990s, the Navy became embroiled in the “Tailhook” scandal in which naval pilots were accused of sexually abusing female officers at a Las Vegas convention. Also, about two dozen female service members were reportedly sexually assaulted during Desert Storm, when U.S. troops helped drive Iraq’s Saddam Hussein from Kuwait in 1991.

Women are still barred from many combat roles, including the infantry. Allowing women to join most military units never produced the kind of backlash or decline in military effectiveness that opponents predicted.

By the time President Bill Clinton proposed allowing gays to serve in the military in 1993, gays had been explicitly barred from military service since World War I.

Foes of lifting the ban argued that the military shouldn’t be used to expand the rights of gays and that allowing them to serve openly would hurt troop morale and a unit’s ability to fight, the same arguments used against women and blacks.

In the end, Congress agreed to let gays serve only if their sexual orientation remained secret.

Today, advocates say they believe history has shown that U.S. troops could handle any disruptions caused by lifting the ban. Opponents of repealing “don’t ask, don’t tell” say letting gays serve openly in the military is different from earlier struggles over the equality of race and gender. Open gay service, they say, raises unique moral questions, such as whether gay and straight troops should be forced to share living quarters.

Senate Majority Leader Harry Reid, D-Nev., was expected to try to force a vote in early December, following testimony by Defense Secretary Robert Gates, Joint Chiefs of Staff chairman Adm. Mike Mullen and service leaders before the Senate Armed Services Committee on Thursday and Friday. The House has passed the legislation.

Much of the debate is likely to hinge on the results of the Pentagon study, with many senators saying they wanted to see whether troops would support such a change before voting for repeal. Still, it’s far from clear whether the bill would even advance to a floor debate with Democrats and Republicans disagreeing on procedural grounds.

Online:

Gates transcript when review panel announced: http://tinyurl.com/28e2cb5