At a time when companies place a premium on teamwork and interpersonal skills, how you view events that affect you and communicate your needs and desires can profoundly influence your effectiveness at work. To put it simply, workplace success is largely about what you say and how you say it.

But many professionals and executives are woefully lacking in good communication skills. They speak in ways that sometimes alienate, confuse or offend co-workers, subordinates and customers and fall far short of achieving the desired result.

To be perceived as a contributor, you must be able to achieve your goals at work without antagonizing others. This lesson can be learned at any point in a career, and will serve you well for the remainder of it. A good place to start is by knowing the differences between being assertive, passive and overly aggressive.

In a brochure designed to help students, the counseling center at the University of Illinois at Urbana-Champaign defines assertiveness as the ability to express yourself and your rights without violating the rights of others. According to the pamphlet, assertiveness is "appropriately direct, open and honest communication which is self-enhancing and expressive."

Aggressiveness, on the other hand, is communication meant to control and dominate others. "It's often destructive in that it provokes anger and resentment and may lead to the loss of respect by co-workers and subordinates," the brochure states.

Passivity at work is the inability to feel comfortable guiding your destiny. Passive people have a sense of unworthiness in their work, aspirations and desires. They convey a lack of confidence and the sense that their ideas, opinions and feelings aren't important.

Jim Schefter, Park City, Utah-based author of "The Race: The Uncensored Story of How America Beat Russia to the Moon" (1999, Doubleday), notes that most NASA project leaders were excellent managers of people. They usually achieved their objectives with gentle but effective persuasion, he says.

Occasionally, some NASA managers failed spectacularly, says Mr. Schefter. "In my research on the space race, I found examples of people who aggressively dominated others out of a need to control events," he says. "Even when they were shown to be wrong and the missions they were in charge of went badly, their styles of communication were usually autocratic, domineering and overpowering. Their results were often spectacularly good, but consistency was always questionable and the alienation of team members was unusually high."

Some employees confuse assertiveness with aggression. In their efforts to achieve goals, they may be too domineering and abrasive and rub people the wrong way, says Rhonda Schonberger, a San Diego design consultant who lectures on assertiveness.

"When they try and do what other successful people do to help their careers along, they're often accused of being too pushy," says Ms. Schonberger. "As a result, they always wonder if even small amounts of assertiveness are viewed as aggression."

Failing those choices, some employees opt for passivity. These types of people are unable to get others to take them -- or their goals -- seriously at work. Their inability to be assertive may be related to insecurity and low self esteem. They feel so diminished that it's difficult for them to establish and follow through on a personal agenda. Their efforts to achieve objectives often result in conspicuous failures.

Because of the value companies place on cooperation and teamwork, you must know how to establish and achieve an agenda at work without being overly aggressive or passive. Using assertiveness techniques may help.

Realize that assertiveness is based on principles or rights. They include:

• the right to our own values, beliefs, opinions and emotions
• the right to tell others how we wish to be treated
• the right to express ourselves
• the right to ask for information or help
• the right to change our minds and to make mistakes
• the right to like ourselves even though we aren't perfect

Translating those rights into acceptable behavior at work requires understanding and practice. The following techniques are considered essential for assertive behavior.

The following statements would project assertive behavior: "I want to..."; "I like it when you..."; "I have mixed feelings about your proposal. I agree with these aspects of it for these reasons, but I don't agree with other aspects of the proposal for these reasons..."

Employees who behave aggressively would use words meant to demean, dominate or show superiority over others. Here are a few examples: "Do what I've asked you to do or else..." and "I know more about it than you do, so do it my way."

"Workers who are overly passive would conclude that their goals aren't valid and might say, "My views aren't important," "You know more about it than I do" or "I guess everyone has a better idea than me."

Knowing how to be assertive is particularly important in sales. Most successful sales people use assertive behavior and treat co-workers, subordinates and customers with respect, says James Toy, a San Francisco women's sporting apparel wholesaler. They keep customers for the long run by using tact and honesty and offering exceptional service.

Occasionally, an aggressive salesperson will appear to be more successful in winning customers, but eventually, their behavior undermines their success, he says.

"Some people in my line of work out sell me for a period of time by being very aggressive, but in the long run, the large corporate customers I deal with resent it," he says.

Mr. Toy says that he sometimes finds the balance between being too passive or assertive with customers is a fine line. "When I'm too passive, I defer my opinions and fail to let others know how I really feel," he says. "When I'm too aggressive, I tend to force my views on others. Neither approach works very well. Subordinates and customers want to know how you feel. They value your knowledge and want to develop a trusting relationship with you."

Deliver your message directly to the proper recipient. Don't use go-betweens or the group to transmit a message you can personally deliver. Aggressive people often act as go-betweens because they enjoy others' discomfort and the sense of power they gain from doing somebody else's dirty work. Passive people permit the use of go-betweens because it helps blunt their message and minimize their being forced to defend their beliefs. Go-betweens also support the view that the passive employee is too unimportant to receive direct feedback.

Ms. Schonberger advises against ever using go-betweens, since it usually creates trust problems. "I try and be direct with people on the job," she says. "Using a go-between usually means that you have something to hide or you lack the courage to give feedback directly. Either way, it creates ill will."

Ask others if your message was clear. If advised that it wasn't, ask for help in clarifying what you said. Encourage others to be clear, direct and specific when they give you feedback. Aggressive people mainly are interested in having others do what they're told. They devalue discussion and feel insecure when others express opposing opinions. Passive people dislike feedback since any form of criticism reinforces their low self esteem.

Good managers often can tell which employees will be successful by the way they accept feedback, says Dr. James Larson, chair of the department of sociology at the University of North Dakota in Grand Forks. Otherwise good students who have difficulty accepting feedback often have difficulty in their careers, he says.

Those who will do poorly at work "often confuse feedback with criticism. Their feelings are hurt, even when the feedback is gentle, and you often don't see them in class for a few days," he says. "This inability to accept and use feedback is generally a sign of serious problems to come."

If you disagree with someone else's perception of an issue, don't tell them that they're wrong. Instead, let them know that you hold a different view and express it reasonably and logically.

Aggressive people often have difficulty seeing other points of view. They frequently become anxious and move to squelch an opinion that differs from theirs because they view it as a form of personal rejection. Passive people don't feel they have a right to an opinion and are unlikely to share one or disagree with others' views.

With today's highly educated workforce, it's critical to be able to listen to and express differences of opinion, says Bill Deitrich, a builder in Austin, Texas. Dr. Deitrich, a former college professor, says he tries to value employees' ideas and involve them in decisions.

"Most young workers expect to be treated with dignity and respect," he says. "If you become overly aggressive with them, they may smile and act as if it's OK, but they often shut down and do badly on the job."

If you have problems controlling your need to dominate or a fear of letting people know what you want at work, consider enrolling in an assertiveness training seminar. In most communities, excellent low-cost courses are available through local continuing education programs, community colleges or counseling organizations.

-- Dr. Glicken is professor of graduate social work at California State University, San Bernardino